FULL REPORT

Pelagic Fish









Lead Author: 

Alistair J Hobday 1

Co Authors: Tim Ward2, Shane Griffiths3

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Alistair Hobday - Pelagic Fish


Author: Marine Climate Change 2012
Dr Alistair Hobday is a Principal Research Scientist at CSIRO Marine and Atmospheric Research. His research spans a range of topics, including spatial management and migration of large pelagic species, environmental influences on marine species, and | Time: 6.13 min

What is happening?

Increased reporting of tropical species from southern waters indicates distributions may be expanding south.

What is expected?

Increased occurrence and persistence of tropical species in southern waters as waters warm.

What we are doing about it?

There is increased modelling of distribution and abundance to refine understanding of impacts for tropical species, coastal small pelagic species, and large offshore species, and thus incorporate impacts of climate change into fisheries management.

Summary

Pelagic fishes and sharks occupy surface waters from the coast to the open ocean. There are ~260 pelagic species around Australia. While some of the most well known are the large offshore apex predators such as tunas, billfish and sharks, the mid-trophic level small pelagic species, such as sardines, anchovies, and squids, are critical to ecosystem function. In Australia, both small and large pelagic species have high ecological, economic and social value. Observed impacts of climate change are restricted to changes in local abundance and distribution, particularly southward range extensions. Little is known regarding changes in phenology, physiology or community structure. In future, general ocean warming around Australia and in particular on the east coast, in combination with predicted strengthening of the East Australian Current, is likely to see the distribution of a range of pelagic species extend southwards from present limits. Recent years have seen a number of reports of fish detected south of their typical range limits on the east coast. On the west coast, changes in the strength of the Leeuwin Current are likely to have major implications for the distribution and abundance of some species, including western Australian salmon and Australian herring in waters off South Australia. Recent extreme events on the west coast have also seen pelagic species reported far to the south of their normal distribution. Changes in productivity, for example due to increased coastal upwelling, may lead to increases in abundance of some species, particularly of small coastal pelagic fishes, such as sardines and anchovy, in the upwelling system between Cape Otway and the central Great Australian Bight. Confidence in observed impacts is generally low to medium as observed changes are limited. Similarly, confidence in future impacts is also generally low to medium, as lack of data on observed impacts makes prediction difficult. Impacts on sharks are poorly known compared to teleost fishes. Overall, impacts in southern Australia are more commonly reported than in northern Australia. Knowledge gaps include an absence of information on species habitat tolerances and methods to detect changes. Recent efforts to develop empirical models for future prediction of species ranges and potential abundance changes are in agreement with earlier projections (Report Card 2009). The adaptation potential is high for many species because of significant opportunity for large-scale movements of most pelagic species, and thus the main impacts are likely to be localized changes in the composition of pelagic fish community. The impact of such changes in community composition is unknown. To address knowledge gaps, focused regional studies on the relationship between climate variables and the distribution and abundance of species of high interest are one way to improve understanding of the potential impacts of climate change. Predictive modelling at appropriate scales is also reliant on downscaled climate models, which can generate a range of environmental variables at the scale of individual fish movements.

Citation: Hobday, A.J. et al. (2012) Pelagic fishes and sharks. In A Marine Climate Change Impacts and Adaptation Report Card for Australia 2012 (Eds. E.S. Poloczanska, A.J. Hobday and A.J. Richardson). Retrieved from www.oceanclimatechange.org.au [Date]

Contact Details: 
1 CSIRO Climate Adaptation Flagship, Hobart, Tas, 7001, Australia.
2 South Australian Research & Development Institute, PO Box 120, Henley Beach, SA 5022, Australia; School of Earth and Biological Sciences, Adelaide University and School of Biological Sciences, Flinders University, SA, Australia
3 CSIRO Marine and Atmospheric Research, Brisbane Qld, Australia

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Authors

Alistair Hobday

Hobday head shot

Dr Alistair Hobday is a Principal Research Scientist at CSIRO Marine and Atmospheric Research. His research spans a range of topics, including...
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Tim  Ward

Ward tim pelagicfish

Associate Professor Tim Ward conducts research to support the ecologically sustainable utilization and conservation of living marine resources. His...
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Shane  Griffiths

Shane griffithsth

Dr Shane Griffiths has been a Research Scientist at CMAR for the past 7 years since completing his PhD at the University of Wollongong in 2002....
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Scientific Review:

Pelagic species occupy the open ocean, which is the largest ecosystem on earth, comprising around 70% of the planet’s surface. Wide-ranging iconic species including tuna, billfish (swordfish and marlin) and sharks are the best known pelagic fishes. However, smaller species, such as sardines and anchovies, are crucial elements of the pelagic realm and are particularly sensitive to impacts of climate variability and climate change (e.g. Jacobsen et al. 2001, Chavez et al. 2003).

Pelagic fishes can be categorised in several ways. For example, small pelagic species, with adult body size <50 cm, and large pelagic fishes, with adult body sizes >1 m, have been distinguished. Species with adults between these sizes, such as skipjack tuna, are typically grouped with large pelagic species. Offshore (oceanic) and coastal (neritic) groups are also often identified, with small pelagic fishes most commonly found in shallow embayments and shelf waters and large pelagic fishes ranging widely offshore, including continental shelf waters and the open ocean. Small pelagic fishes typically occupy intermediate trophic levels, whereas large pelagic species are typically high-level or apex predators (Hunt and McKinnell 2006).

In Australian waters, there are distinct tropical and temperate assemblages, with the dynamic line of integration between the two groups located approximately between Shark Bay and Exmouth Gulf on the west coast and Hervey Bay and Moreton Island on the east coast. In the tropics, different assemblages of small pelagic fishes occur in the Great Barrier Reef, Gulf of Carpentaria, across Northern Territory and the North West Shelf. In temperate Australia, pelagic fish assemblages can be best divided into eastern, southern and western groups, where the dominant oceanographic features are the East Australia, Flinders and Leeuwin Currents, respectively.

Offshore large pelagic fishes

The oceanic pelagic fishes that occur in waters overlying the Australian continental shelf include tunas (e.g. Thunnus spp., Katsuwonus pelamis), swordfish (Xiphias gladius), billfish (i.e. marlin, sailfish and spearfish) and pelagic sharks (e.g. blue shark, Prionace glauca and white shark, Carcharodon carcharias). Many of these species occur throughout the southern hemisphere and have the ability to reach depths of 1000 m, but are generally found in the upper waters of the ocean (0-200 m) (Figure 1). Within Australia, large pelagic species have particular depths that are commonly occupied and prey sizes that are eaten (Young et al. 2010; Figure 2).

The east coast of Australia between southern Queensland and Lord Howe Island has been identified as a biodiversity ‘hotspot’ for large pelagic fishes (Worm et al. 2003). Unlike most of the world’s hotspot regions, where catch rates are relatively low, the Australian biodiversity hotspot for pelagic fish on the east coast of Australia is located in an area of high catch rates and fishing effort (Campbell and Hobday 2003, Campbell 2008; Dell et al. 2011).


Figure 1. Conceptual scheme of the spatial distributions of five dominant taxa in latitudinal water masses (YFT, yellowfin tuna; BET, bigeye tuna; ALB, albacore tuna; SWO, swordfish; BFT, all bluefin tuna species). Depth is divided into epipelagic (water mass from the surface to the mixed layer depth) and mesopelagic (from the mixed layer depth to 1000 m) zones. Source: Reygondeau et al. (2011)


Figure 2. Schematic representation illustrating how the major pelagic fish predators off eastern Australia divide their pelagic habitat over the diel period with respect to depth, prey type and prey size. Their positions reflect a generalised view of their vertical distribution in the water column at times and depth when they are likely to be caught by a longline fishery in Eastern Australia. (Prey lengths are compared over a 50 cm range) Source: Young et al. 2010.

Coastal large pelagic fishes – tropical species
In tropical waters of Australia, the coastal large pelagic fishes comprises around 50 species of tunas, mackerels, billfishes and sharks. The most abundant tropical species use pelagic habitats within the confines of the continental shelf in waters <200 m. These include longtail tuna Thunnus tonggol, mackerel tuna Euthynnus affinis, Spanish mackerel Scomberomorus commerson, Indo-Pacific sailfish Istiophorus platypterus and black tip sharks Carcharhinus tilstoni and C. sorrah. Several other species are reasonably common, including cobia Rachycentron canadum, grey mackerel Scomberomorus semifasciatus and dogtooth tuna Gymnosarda unicolor. However, these species are more commonly associated with deepwater reefs, rather than open water.

Coastal large pelagic fishes – temperate species
The large pelagic fishes of temperate coasts includes several species that are the sole or main local representative of their family including tailor Pomatomus saltatrix (Pomatomidae), eastern and western Australian salmon (Arripis trutta and A. truttaceus, Arripidae), barracouta (Thyrsites atun, Gempylidae), snook (Sphyraena novaehollandiae, Sphyraenidae) and silver trevally (Pseudocaranx dentex, Carangidae). Although there are, or at least have been, significant commercial fisheries for these species in several locations, they are now taken mainly by recreational fishers. Significant commercial fisheries for western Australian salmon still occur off Western Australia and South Australia, mainly for use as bait in rock lobster pots, but overall both species of Australian salmon are now more important to recreational fishers than to commercial fishers.

Small pelagic fishes (temperate and tropical)
Australia’s coastal small pelagic fishes, which are often surface-schooling, includes several families which are often each represented by several species (see Allen 1997, Randall et al. 1997, Gomon et al. 2008), including the Clupeidae (sardines, herrings and sprats), Engraulidae (anchovies), Carangidae (scads, jack mackerel), Scombridae (short mackerels), Atherinidae (hardyheads, silversides), Arripidae (Australian herring) and Emelichthidae (redbait). There are distinct tropical and sub-tropical assemblages of small pelagic fishes, and differences within each of these regions in patterns of distribution and relative abundance (Kailola et al. 1993).

In temperate Australia shelf waters, as elsewhere in the world, the globally-distributed sardine Sardinops sagax is the most abundant species. At least several thousand tonnes of sardine have been taken in a single year from waters off the east coast (NSW and Victoria), South Australia and southern Western Australia (e.g. Kailola et al. 1993, Ward et al. 2006). Several other species with broad global distributions, including redbait, blue mackerel, jack mackerel, and yellow tailed scad, are also abundant in shelf waters in some parts of temperate Australia (Jordan 1994, Jordan et al. 1992, 1995, Lyle et al. 2000, Neira et al. 2008, Ward et al. 2009). At different times, there have been large biomasses and fisheries for jack mackerel and redbait off the east coast of Tasmania (Jordan et al. 1992, Kailola et al. 1993, Neira et al. 2008).

A suite of very small pelagic species, including Australian anchovy (Engraulis australis), whitebait (Hyperlophis vittatus) and blue sprat (Spratelloides robustus), usually dominate temperate, shallow-water embayments, such as South Australia’s two gulfs and Port Phillip Bay (Hoedt and Dimmlich 1995, Dimmlich et al. 2004; Rogers et al. 2003, Rogers and Ward 2007). These species typically have more restricted distributions than the larger shelf species. For example, while the anchovy genus Engraulis occurs globally, E. australis is only found in Australian waters. Similarly, the genus Hyperlophus (two species) is endemic to temperate Australia. Although the Australian anchovy is usually found in inshore embayments, when the abundance of sardine in shelf waters of South Australia was reduced by two mass mortality events in the 1990s, anchovy quickly expanded its distribution into and increased its abundance in shelf waters (Ward et al. 2001b). This change in the species composition of the pelagic fish assemblage in shelf waters is reminiscent of the decadal fluctuations in the relative abundance of anchovy and sardine that have occurred in the eastern boundary current systems off the Americas and southern Africa (e.g. Luch-Belda et al. 1992).

By contrast with temperate waters, the biomass and fisheries of small pelagic fishes in tropical environments are not usually dominated by one or two highly abundant species. For example, Scombrids (Rastrelliger, Scomberomorus), carangids and tropical sardines (Sardinella, Decapterus) all contribute significantly to commercial landings in South East Asia (FAO 1997). Many species such as short mackerels (Rastrelliger), scads (Decapturus) and tropical herrings (Herklotsichthys) are widespread in shelf waters throughout the Australian tropics. Similarly, several species of tropical herrings, Herklotsichthys, occur throughout the Australian tropics, mainly in inshore waters. By contrast, several species of tropical sardine, Sardinella, and two species of Amblygaster only occur in coastal and shelf waters between the Gulf of Carpentaria and the North West Shelf. Similarly, several species of hardyheads (atherinids) are found only on Great Barrier Reef.

Multiple stressors

Commercial fishing is the main stressor on pelagic ecosystems around Australia. Several offshore fisheries capture species that are classified as fully exploited such as southern bluefin tuna and Indian and Pacific Ocean bigeye tuna (Larcombe and McLoughlin 2007). The status of other pelagic species, such as swordfish, is uncertain, while others are classified as underfished (e.g. yellowfin tuna). As part of these legal commercial fisheries, bycatch of other pelagic species such as sharks and sunfish remains a concern, with too little known of impacts and stresses. Illegal fishing for sharks in northern Australia remains a threat. Offshore waters are relatively safe from other anthropogenic impacts such as pollution and habitat modification, although open ocean oil spills may occur and threaten pelagic species (Game et al. 2009). The impact of chronic oil spillage into the surface of the ocean as part of day-to-day boat operations is unknown. A recent publication reporting the detection of radio-nucleotides in migrating Pacific bluefin tuna (Madigan et al. 2012) – resulting from the nuclear accident at Fukushima Japan – suggests sub-lethal impacts for humans and for tuna, however, accumulation of such stressors may become an issue in future.

In northern Australia, three types of fishing stressors have an impact on pelagic fish assemblages: domestic commercial fishing, recreational fishing, and Illegal, Unregulated and Unreported (IUU) foreign fishing. The primary commercial fisheries that target pelagic fishes are the Northern Territory and Queensland Spanish mackerel fisheries (primarily line fishing), and the offshore gillnet fishery that targets sharks and grey mackerel Scomberomorus semifasciatus. The recreational fishery in northern Australia is expanding rapidly, primarily due to expansion of the mining industry and tourism in the region. The efficiency of this fishery is also rapidly increasing, as more sophisticated sonar, radar and GPS become available and affordable, resulting in total catch of some pelagic species being similar to commercial fisheries (Griffiths et al. 2010). The primary target of many recreational anglers is Spanish mackerel and longtail tuna, although there is increasing interest in sailfish and black marlin in regions such as Gove, Groote Eylandt, Weipa and Darwin. The foreign IUU fishery is believed to have had a significant impact on the pelagic fish assemblages in the region, primarily on large sharks, which they target for their valuable fins (Salini et al. 2007, Griffiths et al. 2008). Given that the IUU fishery employ methods similar to the Taiwanese fleet that operated legally in Australian waters during the 1970s and 1980s (Stevens and Davenport 1991), they are also likely to have a significant impact on other species caught as bycatch, including longtail tuna, Spanish mackerel, cobia and sailfish.

Although significant catches of Australian salmon (>1000 t per annum) have been taken historically in several Australian states (Western Australia, South Australia and NSW), the current commercial fisheries for coastal large pelagic fishes in temperate Australia are generally small. Small quantities of Australian salmon, tailor, barracouta, snook, silver trevally and mulloway are taken by commercial fishers in several regions, mainly for local consumption. However, these species of large pelagic fishes in temperate coastal areas are all socially and economically important to the recreational fishing industry.

In temperate Australia, stocks of small pelagic fishes have, in the main, been lightly exploited. However, significant fisheries for small pelagic species currently operate off South Australia (sardines, catches of 30000-34000 t since 2006), around Tasmania (redbait, catch of ~7000 t in 2007) and off the east coast of Australia (sardine, catch of ~3000-5000 t since 2003/04). Declines in the abundance of sardine off Western Australia and jack mackerel off eastern Tasmania have been in part attributed to fishing, but may also have been associated with impacts of climate change. The most spectacular reductions in the abundance of a small pelagic species in temperate Australia were the mass mortalities of sardine in 1995 and 1998/99, which each killed up to 70% of the adult population, and may have been caused by the anthropogenic introduction of an exotic herpes virus (e.g. Whittington et al. 2008).


Observed Impacts:


Expected impacts of anthropogenic climate change on pelagic fishes can mainly be gleaned from known relationships with historical climate variability. No Australian studies have considered the potential changes in the phenology, physiology or community structure of pelagic species. The limited evidence that has been gathered linking climate variability to changes in the abundance and distribution of Australian pelagic fishes is discussed below.


Changes in distribution of pelagic fishes

The known relationships between the distribution and abundance patterns of some large pelagic species on the east coast suggest that changes in the strength of the East Australian Current (EAC) would have dramatic effects on the distribution of a variety of pelagic species. The seasonal extension and retraction of the EAC is linked to the local abundance of species such as yellowfin Thunnus albacares and bigeye tuna T. obesus captured in the east coast longline fishery (Campbell 2008). An increased southward penetration of the EAC may increase the suitable habitat for these species (Hobday 2010; Hartog et al. 2011). At a finer scale, the distribution of yellowfin tuna has been linked to the distribution of mesoscale environmental features such as eddies generated by the EAC (Young et al. 2001). Again, an increase in the strength of the EAC may result in increased eddy formation; these are productive feeding grounds for a suite of species, including yellowfin tuna (Dell et al. 2011). Warm east coast Tasmanian waters in 2010/11 led to a number of pelagic species reported further south than typical, including skipjack tuna, yellowtail kingfish, and striped and black marlin (www.redmap.org.au). These southern occurrences represent the first stages of a range expansion and are likely to become more common in future.


There was extreme warming along the west coast in February and March 2011, with surface temperatures 3-5°C warmer than long-term monthly averages (Pearce et al. 2011). This event - termed a “marine heat wave”- coincided with an extremely strong La Niña event and a record strength Leeuwin Current. The event is considered a major temperature anomaly superimposed on the underlying long-term ocean-warming trend (Pearce et al. 2011). Changes in distribution and local abundance were reported from a range of taxa (Pearce et al. 2011), including pelagic species. For example, one commercial fisher from Albany reported encountering tropical species, such as manta rays, tiger sharks, whitespotted wedgefish, and Spanish mackerel along the temperate south coast (Ryan Bradley, pers. comm.). These responses to extreme events provide additional evidence that range changes in response to warming waters are likely to occur in future.


Few studies have examined movements of coastal large pelagic fishes in northern Australia from which the effects of climate change can be inferred with respect to potential changes in species distributions. However, a recent two-year study of Indo-Pacific sailfish and black marlin using pop-up satellite tags off Gove, N.T. (S.P. Griffiths, unpublished data) revealed that fish have a habitat preference of water temperature of 26-32°C and a tendency to remain within a restricted home range for extended periods and to return to these locations after larger-scale movements of 200-300 km. Similarly, Stevens et al. (2000) showed that carcharhinid sharks (mainly Carcharhinus tilstoni, C. sorrah and C. macloti) have limited movement in northern Australia, with most animals moving less than 50 km after being at liberty for up to 18 years (CSIRO 2002). Similarly, stock structure and movement studies of Spanish mackerel Scomberomorus commerson (Lester et al. 2001, Moore et al. 2003, Newman et al. 2007) show there is limited movement and the presence of several stocks in the region. By contrast, length-frequency and limited tagging data suggest that longtail tuna Thunnus tonggol uses waters off northwestern Australia as a juvenile ‘nursery’ habitat and undertake an ontogenetic movement southward, where they exist as adult fish along the east and west coasts of Australia (Serventy 1942, Stevens and Davenport 1991, Griffiths in review). Here it is believed fish undertake seasonal movements moving north and south, with the expansion and contraction of the East Australian and Leeuwin currents (Serventy 1956, Wilson 1981). A recent study of longtail tuna using pop-up satellite tags (Griffiths, unpublished data) confirmed that fish moved north and south along the coast with the EAC and preferred temperatures of 18-22°C. Evidence from these movement studies indicates that effects of climate change are likely to be species-specific. The most obvious effects are likely to be detected in species that move large distances with seasonal changes in water masses (e.g. longtail tuna). Ocean warming may increase the strength of coastal currents and extend the distribution of highly mobile fish southward.


As species change range at different rates, opportunities for hybridization are enhanced. Hybridization between two species of blacktip shark (Carcharhinus tilstoni and C. limbatus) has been recently reported and attributed to changing distribution as a response to climate change (Morgan et al. 2011). Implications of hybridization are unknown, and might be considered an “adaptation” by species to climate change, as the southern species is gaining “genetic material” from warm-adapted northern species.


Numerous studies throughout the world have shown that small pelagic fishes are particularly sensitive to climate variations (e.g. Jacobsen et al. 2001, Chavez et al. 2003). Both the geographical boundaries between species distributions and the dominant species within an ecosystem vary at decadal scales and be correlated with environmental variability (Lluch-Belda 1992, Stenseth et al. 2004). Anthropogenic climate change will have different effects on small pelagic fish assemblages in tropical and temperate Australia. Alterations to the East Australian, Leeuwin and Flinders currents will be key drivers for small pelagic fishes off the eastern, western and southern coasts, respectively. Along the top-end (effectively the NT), in the Gulf of Carpentaria and in other shallow embayments around Australia, the most significant climate change impact is likely to be a direct increase in water temperature.


Increased sea surface temperatures associated with the greater southward intrusion of the boundary currents along the east and west coasts, may have resulted in the increased southward extension of the distribution of tropical and sub-tropical small pelagic fishes. For example, Sardinella became more prevalent in catches of purse-seine fishers of the south-western Western Australia in the late 1990s. It was hypothesised that this change could reflect a southward extension of the distribution of this species due to increased strength of the Leeuwin Current, and by a local decline in the abundance of the southern sardine species, due to combined effects of over-fishing and mass mortality events (Gaughan and Mitchell 2000). Similarly, off eastern Tasmania in the 1990s, the cold-water species jack mackerel was replaced by the EAC species, redbait, which is consistent with the warming trend observed in temperature records (Ridgway 2007). However, declines in the growth rates and age structure of fishery catches of jack mackerel could have had both environmental and anthropogenic components (Lyle et al. 2000). Changes in the fishing method (purse-seine to mid-water trawl) also confounded detection of environmental relationships (Lyle et al. 2000).


The most likely effect of climate change on tropical species is the southward extension of their current distributions. Increases in water temperatures in shallow temperate embayments are likely to favour species with tropical affinities, such as the blue sprat Spratelloides robustus (Rogers et al. 2003). However, many species in these environments, e.g. anchovy and sandy sprat, are eurythermal (e.g. Ward et al. 2003, Dimmlich et al. 2004) and may be able to cope with quite large increases in water temperature. To date, there is no evidence to suggest that small pelagic fishes of tropical Australia have been adversely impacted by climate change.


Changes in local productivity

In southern Australia, juvenile southern bluefin tuna (SBT) have been the subject of several studies investigating distribution and abundance relationships to mesoscale environmental variability (Hobday 2001, Cowling et al. 2003) or to prey (Young et al. 1996; Ward et al. 2006). In general, environmental linkages to abundance are not strong at the mesoscale, although problems with the spatial resolution of some biological data have confounded analyses (Hobday et al. 2004). Seasonal changes in the abundance of juvenile SBT (ages 1-5) in southern Australia are well documented. SBT are resident along the shelf during the austral summer (Cowling et al. 2003) and then migrate south during the winter. Interannual variation in SBT abundance within the main fishing grounds in the Great Australia Bight has not been linked to the environment, although variation in the arrival time of schools has been attributed to unspecified environmental factors (Cowling et al. 2003). Finally, the impact of climate change on the winter SBT feeding grounds in the Southern Ocean may be more dramatic than those in temperate coastal Australia waters (e.g. Sarmiento et al. 2004).


No increase in productivity has been observed in tropical Australia and no changes in structure or function of assemblages of pelagic fishes that could be related to climate change have been observed. No major changes in productivity are predicted for tropical Australia under most climate change scenarios.


In southern Australia, the most important current is the Flinders Current, which is a cold, current that flows westward along the continental slope and is upwelled during summer-autumn between Cape Otway and the head of Great Australian Bight (Middleton and Cirano 2002). It is predicted that anthropogenic climate change may result in increases in the strength and frequency of the south-easterly winds that prevail during summer and autumn and drive upwelling. The increase in nutrient enrichment that results from upwelling supports the highest levels of primary, secondary production and fish production in Australian waters (Ward et al. 2006). Strongest upwelling events recorded in the Flinders Current system have occurred during the past decade (Neiblas et al. 2009). The rapid increase in sardine biomass in this region since the mass mortality event in 1998 could be in part related to enhanced productivity of this system due to increased upwelling.


Variation in the availability of prey (sardines and anchovies), which are likely if climate change affects the strength of upwelling favourable winds in southern Australia (Hertzfeld and Tomczak 1997, Dimmlich et al. 2004, Ward et al. 2006; Nieblas et al. 2009), may also affect the distribution and abundance of large pelagic predators, such as SBT. Another example of how changes in oceanography can affect productivity and propagate upwards to affect predators could be seen in the effects of the change in relative dominance of the East Australian Current and the sub-Antarctic water masses off the east coast of Tasmania in 1989 (Young et al. 1996). In this warm (La Niña) year, the krill Nyctiphanes australis disappeared from the shelf ecosystem as did their key predator jack mackerel Trachurus declivis (Young et al. 1996). This krill species is a critical component of most Tasmanian shelf foodwebs and persistent warming of the regional oceanography would have a profound effect on pelagic fishes (Young et al. 1996), cephalopods (Pecl and Jackson 2008) and seabirds (Bunce 2004). This change in prey availability has been linked to a change in the relative abundance of two small pelagic fishes (redbait and jack mackerel) in eastern Tasmania (McLeod et al. 2012). The continued poleward extension of the EAC (Hobday and Lough 2011) is expected to favour small warm-water copepods; thus, redbait may have an advantage over jack mackerel due to prey preferences (McLeod et al. 2012). Similarly, oceanographic conditions influence the distribution of krill off southern Australia. Krill swarms that are normally confined to the Bonney Coast between Cape Jaffa and Cape Otway, extend westward into the eastern GAB in years of strong upwelling. During these years, the distribution of blue whales, which come to the Bonney Coast each summer to feed on krill, appears to extend further west into the eastern Great Australian Bight than in weak upwelling years (Ward unpublished data).

The expansion of habitat favoured by tropical small pelagic fishes along the eastern and western coasts would be associated with a concomitant reduction in the habitat available for temperate species, with the northern extent of the distribution of these taxa contracting southward. An increase in the strength of the Leeuwin Current could increase intrusion of tropical species into the GAB. Increased strength of upwelling-favourable winds could increase upwelling of the Flinders Current and enhance productivity in waters between the head of the bight and western Tasmania. This could result in increased production and abundance of existing species of small pelagic fishes, or could cause a major shift in ecosystem structure.

Potential Impacts by the 2030s and 2100s: 


Expected impacts of climate change will be seen first on the distribution and abundance of pelagic species, since water temperature is a key variable influencing the distribution of pelagic fishes (Boyce et al. 2008). Around Australia, the range of many northern species, such as yellowfin tuna is highly likely to expand poleward (Hobday et al. 2008, Hobday 2010), while the northern limit of cool-water species, such as southern bluefin tuna, is projected to contract polewards (Hartog et al. 2011). The impact of changes in other environmental variables, such as salinity, UV, pH and sea level are expected to be minor, based on the known relationships, although some recent work suggests that larval and adult tunas might be vulnerable to increased levels of dissolved carbon dioxide (Nilsson et al. 2012) and oxygen (Wexler et al. 2011). Projections to 2030 and 2100 for particular climate change scenarios show that changes projected for the earlier time period are amplified by the end of the century (Robinson et al. in review).


The timing and extent of the migrations of pelagic fishes may be impacted if there are changes in the timing of expansion or contraction of seasonal currents, such as the Leeuwin or East Australian Current. For example, southern bluefin tuna (SBT) have a seasonal presence along the east coast of Australia (Hobday et al. 2009), which may be restricted further if Tasman Sea warming continues (Hartog et al., 2011). Hobday (2010) described the preferred water temperature for a suite of large pelagic fishes (tuna, billfish, sharks) and then predicted that by 2100 suitable habitat would move further south by an average of 4 degrees (~450 km) on the east coast and 3.5 degrees (~390 km) on the west coast. The area of suitable habitat was also predicted to decline on the east coast due to warming, while on the west coast, the area of suitable habitat would be similar due to an expansion into southern Australia (Hobday 2010). Recent work by Robinson et al. (in review) reported somewhat faster rates of movement on the east coast, with the northern range edge moving poleward more rapidly than the southern range edge.


A climate change risk assessment for sharks and rays on the Great Barrier Reef indicated that freshwater/estuarine and reef associated sharks and rays are most vulnerable to climate change (Chin et al. 2010). They reported that changes in temperature, freshwater input and ocean circulation will have the most widespread effects on these species. Such risk-based assessments should be used more widely for pelagic and other species.


Specific future habitat modelling for coastal and small pelagic fishes has not been conducted, but in a similar way, the apparent annual northward migration of sardine, blue mackerel and tailor along the east coast to spawn and/or the transportation of larvae southwards into nursery grounds and adult habitats (Ward et al. 2003) could be affected by changes in the EAC. For example, if winter water temperatures further south warmed, the extent of these northward migrations may be reduced and these species may not migrate into waters off southern Queensland to spawn.


Changes in the physiology of Australian pelagic species might be driven by climate change. Studies in tropical Atlantic and Pacific regions indicate how physiology, changes in climate, and fishing pressure may stress fish populations (Prince and Goodyear 2006; Stramma et al. 2012). Large areas of cold hypoxic water in the eastern tropical Pacific and Atlantic oceans, occurring as a result of high productivity initiated by intense nutrient upwelling, restrict the depth distribution of tropical pelagic marlins, sailfish, and tunas (Stramma et al. 2012). The acceptable physical habitat is compressed into a narrow surface layer. This in turn makes them more vulnerable to over-exploitation by surface fishing gears. If climate change further compresses the habitat, many tropical pelagic species could be quite sensitive to increased fishing pressures (Stramma et al. 2012). In Australia, vertical habitat compression or horizontal expansion may occur as a result of climate-forced ocean changes. In the following sections, the impact of change in particular environmental variables is considered.


Sea Surface Temperature (ocean temperature)

Change in ocean temperature, especially in the surface layers, is expected to have an impact on the distribution and larval survival of many pelagic species. For example, Kimura et al. (2010) suggest that the survivorship of Pacific bluefin tuna Thunnus orientalis larvae may decline by 36% under the IPCC 2007 scenario. Similarly, Wexler et al. (2011) experimentally determined that yellowfin tuna produce larvae of significantly smaller egg diameters in scenarios where SST was increased to >27°C, which may result in fish that are smaller and in poorer condition at-length. In Australia, Southern bluefin tuna T. maccoyii (SBT) are restricted to cooler waters south of the EAC and range further north when the current contracts up the New South Wales coast. This response to climate variation has allowed real-time spatial management to be used to restrict catches of SBT by non-quota holders in the east coast fishery by restricting access to ocean regions predicted to contain SBT habitat (Hobday and Hartmann 2006, Hobday et al. 2009). As observed in recent years, southward movement of large pelagic species such as tropical tuna, billfish and tropical sharks is expected to continue.


Along the eastern and western coasts of Australia, the distribution of neritic tropical large pelagic species is likely to extend further southward. For example, along the east and west coasts the abundance of longtail tuna and various mackerels (Scomberomorous spp.) could increase in temperate locations off New South Wales and southern Western Australia. Conversely, the habitat available and hence the population size for temperate species such as tailor, Australian salmon, snook, and barracouta, may contract as warm water from the tropics extends further south. In parts of New South Wales, this could result in the suite of large pelagic fishes changing from temperate to sub-tropical. Off Tasmania, warm temperate species could become more prevalent.


Off the south coast of Australia, the increased strength of the Leeuwin Current and level of intrusion into the central GAB could introduce additional sub-tropical and tropical species into this region. Cooler sea surface temperatures during summer and autumn in waters between the head of the Great Australian Bight and western Tasmania could enhance the environment for cool temperate species.


Rainfall/Coastal runoff/Salinity

Changes in rainfall and salinity are not likely to influence the large pelagic species in southern Australia, as the change in salinity in the open ocean is expected to be negligible.


By contrast, changes in rainfall and salinity are likely to have a detectable effect on the distribution of pelagic fishes in northern Australia. This is due to numerous large rivers discharging large volumes of low salinity, turbid water into coastal regions where sediment plumes may extend tens of kilometres offshore (Vance et al. 1998). Considering that large pelagic fish rely heavily on their eyesight to feed, they are likely to be forced further from the coast to feed in clearer waters (Griffiths et al. 2007). Because neritic pelagic fishes are restricted to a narrow coastal habitat, constriction of an already small habitat may increase density-dependent mortality within species and increase competition among species that normally spatially partition resources (see Potier et al. 2004). Sharks primarily use their sense of smell and electroreception to locate prey (Moss 1977), so movement of larger teleost fish to offshore waters during the monsoonal season may benefit shark populations as a result of decreased competition for common prey, such as small pelagic fish. Changes in rainfall have also been suggested to increase vulnerability of northern sharks to climate change (Chin et al. 2010).


Reduction in rainfall in eastern Australia (Lough and Hobday 2011) could have implications for assemblages in shallow embayments, especially in southeastern Australia where reductions in rainfall may be most significant. Most species that inhabit shallow embayments are adapted to coping with significant variations in temperature and salinity. However, as runoff provides a significant input of nutrients in some regions, reduced rainfall could result in decreases in estuarine productivity.


Wind and upwelling

Wind indirectly impacts pelagic species through mixing of the surface waters (Cury and Roy 1989), although the direction of productivity changes is hard to predict. Pelagic regions may become more or less productive, depending on the relative balance of nutrients, light and stability for phytoplankton production (Cury and Roy 1989, Bakun and Weeks 2004). It is possible that wind may increase mixing of turbid surface waters and have the same effect on fish in northern Australia as rainfall and coastal runoff in that it may affect the ability of fish to locate prey.


Off southern Australia, an increase in the strength or persistence of southeasterly winds between the head of the Great Australian Bight (GAB) and western Tasmania and northeasterlies along the east coast could increase upwelling (Neiblas et al. 2009), which could enhance pelagic production and abundance of some species of small pelagic fishes. However, large increases in wind-forced upwelling can also result in catastrophic consequences for coastal pelagic systems, such as deoxygenation of sub-surface waters and massive die-offs of benthic species (Bakun and Weeks 2004).


The largest upwelling system in temperate Australia extends from the head of the GAB to western Tasmania (Ward et al. 2006, Nieblas et al. 2009). There is also a smaller upwelling system on the east coast, around Smoky Cape. Increases in the strength of winds and boundary currents that drive upwelling in both locations are likely to increase (Nieblas et al. 2009). Some species, such as sardines, blue mackerel and redbait, may benefit if this increase in wind speed leads to increased seasonal upwelling and local productivity. The species and location where an increase in abundance is most likely, is sardine off South Australia where spawning dynamics are strongly linked to upwelling (Ward et al. 2006). However, increased upwelling can also have negative impacts (Bakun and Weeks 2004), including changes in community structure, such as on phytoplankton and zooplankton assemblages, that could in turn affect small pelagic fishes.


Upwelling regions in southern Australia are important foraging grounds for some large pelagic fishes, such as bluefin and yellowfin tuna. If upwelling becomes more intense, and production of small pelagic fishes increases, then aggregation of the large species may increase. In northern Australia, coastal upwelling is a minor process, with no expected impact on the pelagic fishes of the region.


Mixed layer depth

Some large pelagic species are constrained by physiology to remain in the warmer mixed layer (e.g. skipjack tuna). The anticipated changes in mixed layer depth are minor (a few meters) in the regions around Australia (Richard Matear, CSIRO pers. comm), and impacts on open ocean pelagic fishes and sharks may not be detectable, or significant. If the changes in mixed layer depth do result in changes in available habitat, such as vertical compression, then impacts such as changes in fish catch are expected (e.g. Prince and Goodyear 2006; Stramma et al. 2012). Negligible impacts for coastal pelagic fish, both large and small, are expected since they occupy shallow waters (

<100 m) where mixed layer effects are minimal.


Changes in productivity and pelagic fishes

Climate change is altering the rate and distribution of primary production in the world’s oceans (Polovina et al. 2011), although a clear climate signal is not yet emerging (Henson et al. 2010). Primary production is critical to maintaining biodiversity and supporting fishery catches, and modelling attempts to date have shown variable responses, depending on the species of interest. Brown et al. (2010) simulated the effects of change in primary production on diverse marine ecosystems across a wide latitudinal range in Australia using the marine food web model Ecosim, to predict changes in fishery catch, fishery value, biomass of animals of conservation interest, and indicators of community composition. Under a plausible climate change scenario, primary production was projected to increase around Australia, resulting in increased biomass of pelagic fishes and sharks.


Using the same modelling tool, Griffiths et al. (2010) projected changes in the east coast pelagic fish assemblage resulting from projected changes in primary productivity, and prey biomass (microneckton and squid). The simulated increase in phytoplankton biomass due to climate change resulted in only small increases (~11%) in the biomass of all groups, however, possible climate-related changes to the biomass of micronekton fish (-20%) and cephalopods (+50%) resulted in trophic cascades, with large changes in the abundance of pelagic fish. Both studies emphasize the dependence of their results on the underlying productivity changes. As potential productivity changes are poorly understood, there is low confidence in these projected changes in abundance for Australian pelagic fish.

Projected impacts on fisheries based on potential productivity increases suggest that fisheries that rely on pelagic species, and their related sectors, could benefit from climate change (Norman-Lopez et al. 2011).

Key Points: 


• The main climate drivers that will impact pelagic fishes around Australia are water temperature and winds. Increased water temperature will cause changes in species distribution, while increases in upwelling-favourable winds will result in increased upwelling-generated productivity.
• The main impact of change in these drivers on temperate large pelagic species will be on their distribution. The impact on overall population size is less certain, and dependent on changes in primary productivity and prey availability. Exploring climate relationships in offshore waters will be challenging, due to the short and patchy time-series of species abundance data.
• Increased strength of south-easterly winds during summer and autumn is likely to increase seasonal upwelling along the southern coast between the head of the Great Australia Bight (GAB) and western Victoria. This region supports Australia’s largest population of sardines, which is supported by enhanced productivity associated with upwelling. If upwelling increased, the size of the sardine population could increase. However, an increase in upwelling could also have significant negative impacts on community structure and function.
• Increased pelagic productivity and sardine abundance off southern Australia could be beneficial for the southern bluefin tuna that aggregate each year in the feeding grounds of the central GAB. Similarly, increased upwelling off Smoky Cape (NSW) could enhance productivity and aggregation of small and large pelagic fishes off Australia’s east coast.
• The distribution of Australia temperate pelagic species is likely to move southward as water temperatures warm on both coasts, and could result in reductions in available habitat and population size for some species dependent on the continental shelf. Conversely, suitable habitats and hence population sizes, could increase for some tropical species as more of temperate Australia becomes suitable.
• The tropical assemblage of pelagic fishes is likely to extend further south along the eastern and western coasts. Availability of some species at particular locations may change. For example, sardine, blue mackerel and tailor are currently present in southern Queensland and northern New South Wales mainly during winter and autumn due to the northern spawning migration. If winter water temperatures increased significantly, the extent of these migrations may be reduced and these species may no longer spawn in waters off southern Queensland.

Confidence Assessments

Observed Impacts: 


Large pelagic fishes

There is LOW evidence of observed impacts in large pelagic fishes. Long-term data in temperate Australia are limited to fishery-dependent data for a small number of species. There is a LOW level of agreement that climate change is affecting large pelagic fishes; much of the evidence of fish distribution shifts is anecdotal or based on limited evidence of latitudinal changes in the sizes of fish within populations (length-frequency). Very little quantitative data has been collected to base predictions of climate change impacts on temperate or tropical large pelagic fishes in Australia.


We have MEDIUM confidence that climate change is affecting large pelagic fish in the open ocean. No attempt has been made to link abundance or distribution to environmental variables.


Small pelagic fishes

There is MEDIUM evidence with regard to distribution changes in small pelagic fishes. Changes in fishery catches off the east (redbait replacing jack mackerel) and west coasts (Sardinella replacing sardine) are consistent with the hypothesis of southward extension in the distribution of warm water species. There is a MEDIUM consensus with regard to changes in distribution. Fishery data suggesting that southward range expansions of warm-water species along both the east and west coasts of Australian are confounded by effects of fishing and changes in fishing gear.


There is LOW evidence with regard to upwelling changes. Prevalence of historically strong upwelling years over the past decade off southern Australia suggest that upwelling may have increased due to climate change. Rapid recovery of sardine populations off South Australia following mass mortality events suggest strong upwelling years are favourable for sardines. There is a LOW consensus with regard to changes in upwelling. Formal comparisons of upwelling strength over the past decade in relation to historical levels have not been conducted. Ichthyoplankton samples/data have not been analysed to assess potential changes in assemblages of small pelagic fishes that may occur under increased upwelling scenarios.


There is MEDIUM confidence that some small pelagic fishes in warm waters have expanded distributions southwards along the east and west coasts of Australia and that habitat suitable for cool, temperate species has been reduced. There is LOW confidence that rapid increases in the population size of sardine off southern Australia over the last decade can be attributed to increased upwelling due to climate change.

Potential Impacts by the 2030s and 2100s: 


Large pelagic fishes

There is a MEDIUM level of evidence and a MEDIUM consensus that oceanic fishes and sharks will be impacted by climate change. Warming along the east and west coasts of Australia is predicted by a range of general circulation models (Hobday and Lough 2011). Distribution models of fish response to warming suggest that there will be a southward expansion of these fishes on both coasts (Hobday 2010; Robinson et al. in review).

There is a LOW level of evidence and LOW consensus for potential changes in large coastal pelagic species in the tropics. Very little data have been collected, especially over the long-term, to base predictions of climate change on pelagic fishes in northern Australia. Much of the evidence of fish movements is anecdotal or observed seasonality catches of latitudinal changes in length-frequency.


We have MEDIUM confidence for oceanic large pelagic species with regard to movements in response to a warming ocean and LOW confidence for coastal large pelagic species. Distribution models have not been developed for the present or run with climate futures.


Small pelagic fishes

There is MEDIUM evidence and a MEDIUM consensus that tropical assemblages of small pelagic fishes will expand southward and that habitat available for temperate species will contract. Oceanographic models suggest that increased intrusion of the EAC and Leeuwin Current is likely on the east and west coasts, respectively. Observations suggesting that expansion of the distribution of warm-water species along the east and west coasts may already have occurred are moderately robust. Models predicting southward distribution changes in the distributions of large pelagic species over the coming century are also likely to apply to small pelagic species.

We have MEDIUM confidence regarding a southward extension of the distribution of tropical species and a contraction in the distribution of temperate species off the east and west coasts. There is a need to use outputs from physical models and develop and apply distributional models for key species to increase confidence in the nature of changes.

Summary of Confidence Assessments for Observed and Future Changes in Australian Waters


Adaptation Responses

Adaptation can be with respect to the fishes or to the humans reliant on the fishes, for example through fishing or tourism businesses (Hobday and Poloczanska 2009). The adaptation response of pelagic fishes to future climate change is unknown, although based on the evidence discussed above it is anticipated that a change in distribution in response to an altered environment is most likely for a range of species. Genetic responses to climate change may also occur (e.g. hybridization) although the fast pace of climate change relative to the slower rate of evolutionary response may present a significant barrier to biological adaptation. In the remainder of this section we focus on the human side of adaptation to climate related changes in Australia’s pelagic fishes.

With respect to the humans that rely on pelagic species, a range of adaptation responses are possible (Hobday and Poloczanska 2009). Climate change may lead to alternative species being harvested when the primary species is less available. Interaction between the commercial and recreational sectors and other marine users are also resulting in zoning that excludes fishing activities in some areas (e.g. recreational fishing zones, marine protected areas). Current approaches for dealing with changes in fisheries as a result of climate variability include; changes in fishing ports used, changes in fishery areas, changes in the quota allocated for harvest, and closures in some fisheries or fishing areas (Hobday and Poloczanska 2009; Norman-Lopez et al. 2011). The adaptation responses may also differ between offshore large and inshore small pelagic fishes.

Offshore large pelagic fishes

Fishers dependent on pelagic fishes exhibit considerable fish finding skills. Their target species roam widely, and are subject to considerable interannual fluctuations in distribution and relative abundance. To counter this variability, fishers use a range of environmental products, such as satellite information and sophisticated on-board electronic equipment (Hobday and Poloczanska 2009; Dell et al. 2011). These help them to locate suitable conditions for the species that is being targeted. Continued use and improved availability of these products and development of new predictive tools may improve the capacity of the fishers, providing the stocks can sustain the continued or enhanced harvests. In some fisheries, spotter planes also reduce the search time by locating schools of fish (e.g. southern bluefin tuna in the Great Australian Bight, skipjack tuna on the east coast of Australia).

Coastal large pelagic fishes

The primary adaptation response that may be required in northern Australia may be the movement of fishers to more offshore fishing areas and also further south toward the southern extremities of the species current distributions. Movement of fishers offshore would be in response to increased rainfall and runoff into coastal regions, which may force both commercial and recreational fishers to incur greater economic costs to travel further offshore to target pelagic fish such as Spanish mackerel, billfish and tuna. This may decrease economic returns to commercial fishers, but also to local economies that rely heavily on recreational anglers. In contrast, if shark populations increase in inshore regions as a result of decreased competition by pelagic teleost fish, then this may provide increasing opportunity for investment in inshore shark fisheries. In the case of indigenous fisheries in northern Australia, movement of pelagic fishes further offshore may make these species (e.g. Spanish mackerel) inaccessible to fishers. This may result in a switch to species that may become more abundant as a result of reduced competition or predation pressure by predatory pelagic fishes (e.g. sharks or small pelagic fishes).

Southward expansions of distribution, and potential increases in the population size, of some coastal large tropical pelagic fishes could result in the expansion of some fisheries. For example, an increase in distribution and abundance of Scomberomorous spp. could benefit fishers off NSW, and potentially increase the total catch of this species along the east coast. However, this could also complicate management of the Queensland East Coast Mackerel Fishery, by increasing the need to consider catches taken in other jurisdictions. Conversely, contractions in the habitat available to temperate pelagic species could have some implications that would be difficult for fishers to resolve. For example, fishers in southern Queensland that target tailor from the shore or in small boats may have limited capacity to adapt to reductions in the northward extent of this species’ spawning migration that could result from climate change.

With respect to sharks and rays found on the Great Barrier Reef, Chin et al. (2010) propose a range of approaches including mitigating climate change and addressing habitat degradation and sustainability issues. Species-specific actions may be required for higher risk species (e.g. the freshwater whipray, porcupine ray, speartooth shark and sawfishes) including reducing mortality, preserving coastal catchments and estuarine habitats, and addressing fisheries sustainability. These issues are not confined to sharks and rays, and multiple benefits would be attained in pursuing these adaptation efforts.

Small pelagic fishes

Expansions in distribution of tropical small pelagic fishes and contraction in habitats of temperate species could have potentially significant implications. However, localised replacement of cool water species with warm water species may be manageable in some cases. For example, the change of target species from jack mackerel to redbait that occurred off Tasmania did not have catastrophic impacts on the fishery, however fishing practices did change (McLeod et al. 2012). Changing target species may require costly modifications to fishing practices. Impacts of changes in distribution will have the most significant effects when the replacement species is/are of lower value than the original target species. This may require fishers to develop new markets for replacement species. In some cases this may not be possible. If, for example, a tropical species such as Sardinella expanded its distribution along the east coast and effectively replaced sardine off NSW, this would have a major commercial impact on the NSW Ocean Haul Fishery as Sardinella is less valuable than sardine. Developing markets for Sardinella would be difficult. Alternatively, the fleet could travel southward to follow that change in the distribution of sardine. However, this would significantly increase fishing costs and may be logistically impractical. There are also potential jurisdictional issues as sardine is currently managed by the States except in commonwealth waters off NSW. An increase in abundance of sardine off South Australia due to increased upwelling would be relatively simple to manage. However, a change in the structure and function of the pelagic community could have catastrophic consequences.


Observations and Modelling

Many knowledge gaps exist. Much of the information discussed in the earlier sections was based on (short-term) studies of species response to climate variability, rather than (long-term time series) studies that demonstrate a temporal trend that is consistent with a climate change response. With regard to pelagic species, changes in distribution have been documented, although long-term data are sparse. Generation of such time series data may be possible using catch records, although biases in the collection of such data continue to present obstacles. Use of proxy records, such as growth records from fish otoliths (ear bones) or scales, may help to fill some of the gaps (e.g. Thresher et al. 2007). In situ studies that record the relationship between environmental conditions and species abundance, phenology and physiological responses are needed to further understand the adaption responses of the fish to climate change. These studies, particularly if they span a range of conditions, can allow inference about the likely rate of species response to future climate change. Development of habitat-based distribution models for small pelagic fishes, based on ichthyoplankton data for example, can be tested with historical survey data, and then used to make future predictions. Future predictions of species responses are dependent on predictions of future environmental conditions. While sea surface temperature predictions are routinely made, additional mesoscale variables are important to pelagic fishes, particularly changes in upwelling, or the location of oceanic eddies. At this time, global climate models do not represent these features, and so downscaled models must be enhanced (Hobday and Lough 2011; Stock et al. 2011).

Information on the response of pelagic sharks to historical changes is limited compared with the teleost fishes. Northern Australian responses are also less clear. Mesopelagic fishes (depth 200-800 m) were not considered in this section, and as these species are critical prey species for almost all the offshore large pelagic fishes (Young et al. 2009), more information on these species is needed. With regard to human adaptation to changes in pelagic fishes, knowledge gaps relate mainly to how best to improve the flexibility of fishers to sustainably harvest a range of commercial and recreational species. In many cases, adaptation responses may be autonomous and reactive, although having management considering the future changes is necessary now, and may prevent undesirable outcomes (Hobday and Poloczanska 2009).

Observation Programs and Adaptation Actions

With regard to better measuring changes in pelagic species distribution, direct scientific surveys, fishery-dependent data collection (e.g. logbooks), and citizen science projects can all provide information. One citizen science initiative is RedMap (http://www.redmap.org.au), currently focusing on Tasmanian waters, but planned for national release in October 2012. This website allows the public to log sightings of marine species and has already documented evidence of distributional changes in species that has been used in scientific papers (e.g. Last et al. 2011; Madin et al. 2011).

The Integrated Marine Observing System (http://www.imos.org.au) includes the Australian Animal Tracking and Monitoring System (AATAMS), which is a sustained observing system designed to observe movements and foraging activity of higher predators in relation to oceanographic variables. A number of large pelagic fishes and sharks are studied in this program.

The main policy questions for the pelagic species will be around setting sustainable harvest levels, and protection of vulnerable species such as sharks. As species change distribution, patterns of exploitation may change, and result in different interactions between, say, exploited and protected species. Determining any changes in the distribution and abundance of key species should be a focal point for science to inform management. Increased productivity may lead to increased biomass of small pelagic species, which may permit larger harvests in some regions. Because fisheries will move and their methods are likely to change, attribution of change may be difficult. Stock assessment may also be compromised if the fisher behaviour and hence data collection changes quickly (Link et al. 2011).

Although expensive, fishery-independent surveys will provide the best evidence for changes in distribution, abundance, and phenology. These surveys will be relatively easier for coastal small pelagic species, and hardest for offshore large pelagic species. Electronic tagging programs provide the best approach for detecting change in offshore wide-ranging species, and collaborative analysis is important to improve the sample size and geographic coverage (e.g. Hobday and Evans, in press).

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