The potential effects of climate change on southern calamary in Tasmanian waters: biology, ecology and fisheries
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- (2) Population effects
- A) Biomass
- B) Timing of peak abundance
- C) Location of peak abundance and range shifts
- D) Ecosystem effects
- (3) Impacts on the fishery in Tasmania
(C) Adult spawning phaseIt is not clear how elevated temperatures or changes in productivity may alter the reproductive output of southern calamary, and how this in turn may impact on the population dynamics of subsequent generations. Methods for estimating fecundity are poorly developed for cephalopods (Boyle 1990), as is an assessment of how they distribute reproductive effort through time and space (Pecl 2001). However, we know that large-bodied Sepioteuthis that grow through cool conditions will have larger gonads and greater reproductive output compared to their warm wanter counterparts. Warm-water squids will have a greater relative gonad investment with a higher percentage of their body weight as reproductive tissue, even though in absolute terms their gonads will weigh less (Jackson and Moltschaniwskyj 2002, Pecl 2000). However, we don’t know if this potential drop in fecundity will be overridden by increased number of spawning episodes fuelled by a more rapid production of gametes. We currently have no information about how the batch frequency or total number of eggs deposited may be affected by temperature, food availability or life-span. It is likely that food availability may be a more crucial determinant of reproductive allocation (Ho et al. in press, Pecl et al. in press b). Based on what we know from past work, global warming will produce squid that grow faster but have a smaller body size (due to reduced hatchling size and a reduction in the time taken to reach maturity) and mature younger (Figure 4). This in turn will increase physical constraints on just how much gonad a squid can produce. While the warm-water squid will have greater relative gonad investment, each individual will be smaller so absolute gonad output may be less. Furthermore, different sized adult squids could also change the social and behavioural aspects of courtship, mating and egg-laying. (2) Population effectsBecause of the numerous and obviously complex interactions, predicting the potential outcomes of environmental change on discrete populations or species is not straightforward (Clark et al. 2003). No species lives in an ecological vacuum, and although the link between physiology and thermal tolerance can set theoretical distribution limits, the boundaries to geographical ranges are typically set by other factors – including competitive interactions, suboptimal physiological performance (Clarke 2003), and in some circumstances, habitat availability. In the context of the current paper, we are interested in A) potential changes to the absolute biomass of the southern calamary population, B) shifts the timing of peak abundance, C) shifts in the location of peak abundance or alterations to overall distribution or range, and D) the impact of any of these changes on the rest of the ecosystem of which southern calamary are a part. A) BiomassSquid fisheries are well known for their highly variable recruitment and catches, which creates uncertainty for resource managers and the fishing industry, due to increased risk of stock collapse. Large fluctuations in catch of the inshore squid Loligo bleekeri (eg: 40 fold, Natsukari and Tashiro, 1991) are apparently unrelated to fishing effort (Beddington et al. 1990). The population dynamics of cephalopods are principally influenced by phenotypic plasticity in response to environmental variation (Boyle and Boletzky 1996), although the mechanisms and links through which this occurs are not well understood (Pecl et al. in press b). Biomass changes quickly throughout a year and between years, and it is very likely that climate change will have significant impacts on absolute biomass. Although several studies have sought to establish relationships between environmental variables and cephalopod biomass, this has not been overly successful and predictions of cephalopod abundance on an annual basis are not yet possible. This makes sensible suggestions of how biomass may change under a scenario of climate change quite difficult. The absolute level of biomass may be affected by the carrying capacity of the evolving ecosystem. If productivity is decreased for example, the rate of cannibalism within southern calamary populations will likely increase so that fewer individuals will do well, however, biomass may be reduced if the level of cannibalism is high. B) Timing of peak abundanceGlobal warming may alter both timing and location of peak abundance. Timing of peak squid abundance advances by 120-150 days in warmest years compared to coldest for Loligo forbesi in the English Channel (Sims et al. 2001). Cephalopod biomass production is strongly cyclical and usually an annual phenomenon except in some small and or tropical species (Boyle and Boletzky 1996). Climate change will likely result in life-spans that are shorter, and there is the possibility that temporal synchronicity of spawning activities of the population may be reduced. Currently, southern calamary have a 10-12 month life-span (including embryonic stage) and as a function of low levels of spawning all year, and batch spawning of females throughout the main spawning season, squid enter the spawning grounds throughout the spring-summer spawning season in waves of ‘micro-cohorts’ (Figure 5a, Jackson and Pecl 2003). If life-spans are reduced, spawning activities may become less synchronised and the production of biomass may become more complicated (Figure 5b). Shorter life-spans and higher temperatures may even result in almost continuous aseasonal breeding and therefore recruitment as currently occurs in tropical environments (Figure 5c). The synchronisation of breeding activities may however, also be related to other environmental cues such as day length. The manner in which synchronisation of spawning activities, and subsequent effects on biomass, actually alter under a scenario of elevated temperatures (like a sub-tropical or tropical environment) but continued seasonal cues (like day length in temperate environments) remains obviously unknown. Many temperate loliginids lay eggs so that the hatchlings emerge at the peak of production, and while temperatures increase so that hatchlings may grow fast whilst feasting on an abundance of prey (eg: Loligo vulgaris reynauldii, Sauer et al. 1992). Any de-synchronisation of peak spawning and peak productivity may have implications for juvenile growth rate and survival. Spring blooms can be characterised by peak amplitude, timing of peak, timing of initiation and duration (Platt et al. 2003) – how these factors alter in Tasmania with climate change may impact substantially on the success of each years spawning. C) Location of peak abundance and range shiftsClimate change may influence population movements by altering temperature, quality and quantity of food, or in the case of benthic spawning squids, altering the characteristics of the seafloor habitat. The life-style of loliginid squids is intimately linked with the seabed, as they lay compact egg masses attached to the bottom (Boyle 1990). Southern calamary spawning activity is closely associated with Amphibolis seagrass, and any alterations in distribution of spawning aggregations as a function of climate change may be tightly linked to changes in Amphibolis distribution. Species may also avoid warmer waters simply because food supplies are insufficient to maintain such high metabolic rates, as has been suggested for salmon (Welch et al. 1998). Researchers suspect that, as with most other loliginids, deep-water spawning also occurs in southern calamary. As temperatures increase, if southern calamary have distinct thermal preferences they may move further south, to cooler waters, or they may move to deeper waters. We do not have any information about the extent to which any inshore-offshore migrations may take place in southern calamary. There are two genetic types of calamary, and a hybrid, that have been detected within the Australian distribution (Triantafillos and Adams 2001). Southern calamary in NSW are a different genetic type (‘peripherals’) to Tasmania (‘centrals’) (Triantafillos and Adams 2001). With elevated temperatures, or changes in prey distribution and abundance, the ranges of the two types of southern calamary may shift. The genetic type of southern calamary found at higher latitudes may move south to lower latitudes. This could result in a very complex population structure and may impact on the reproductive potential of the population if the two genetic types overlapped, as the hybrids are thought to be reproductively sterile. D) Ecosystem effectsSquid have high production to biomass ratios (O’Dor 1992), and one constraint on their life-cycle is the heavy pressure placed on the ecosystem through predation by large squid populations (Roberts et al. 1998). Predation by a strong cohort of cephalopods on early stages of commercial fish is likely to be a variable affecting the recruitment success of fish stocks (Rodhouse and Nigmatullin 1996). Plainly, large schools of squid can have a very significant impact on fish and crustacean populations. Energy used by a population equals the population density multiplied by metabolic requirements of each individual (Knouft 2002). Individual squid will be eating more per unit size as temperatures increase, so any stock of a given size may place greater demands on the rest of the ecosystem at a higher temperature than at a lower temperature. (3) Impacts on the fishery in TasmaniaWhen considering the issue of climate change and potential effects of this global phenomenon on the life-history, population biology, and fisheries of inshore squid, it needs to be highlighted that different degrees of certainty come into play when discussing various pieces of this complex puzzle. For example, the impacts of elevated temperature on the embryonic duration, size of hatchlings, and growth of adults, are well known and have a solid physiological basis. Thus, many of the ways in which individual components of climate change in isolation may impact on the lives of individual squid can be estimated with a reasonable degree of certainty. However, while population and individual-level processes are intimately linked, we unfortunately have a poor understanding of factors structuring and regulating cephalopod populations. The complexity of ecological interactions renders it very difficult to extrapolate from studies of individuals or populations to the community or ecosystem level (Walther et al. 2002). As cephalopods are ‘ecological opportunists’, it is even more difficult to suggest with any certainty what the impacts of climate change will be on aspects of their population or fishery biology. Notwithstanding the above, this discussion paper raises several issues concerning the potential impacts of climate change on southern calamary life-history and populations, which may have relevance for resource managers and fishers that depend on the resource: If generation times are shorter will southern calamary still exhibit aggregative spawning behaviour? Will spawning aggregations become less spatially and temporally predictable? If synchronicity of spawning activities is reduced, are miss-matches between peaks in spawning activity and peaks in production likely? Changes in the characteristics of spawning aggregations will have impacts on subsequent population dynamics, and also to the fishery itself. Spawning aggregations are very easy and cost effective for fishers to target, if aggregations are less predictable, or less dense will fishers shift to other already overexploited resources? Will the location of peak abundance shift? This could occur either 1/ further south towards the major population centre of Hobart, and away from coastal fishing towns on east coast, or 2/ into deeper and therefore cooler water further away from the coast, and less accessible to small-scale fishers in 6m boats. Will the peak in spawning become harder to predict? Currently the main management objective is to provide protection to spawning adults via short-term closures to ensure each generation deposits sufficient eggs. Any changes in the predictability of spawning activities will necessitate changes to management strategies. Climate change will have substantial impact on the size of individuals, this needs to be monitored and considered in management evaluations as body size will alter correct interpretation of both effort and catch per unit effort (CPUE) assessments of the fishery (Pecl et al. in press b). The effort and CPUE statistics for a population made up of 300g individuals will be very different to that of a population made up of 3000g individuals. If the ‘peripheral’ and ‘central’ genetic types (Triantafillos and Adams 2001) have different thermal preferences, and the distribution of the two types alters in accordance with these thermal preferences, Tasmania could see a different genetic type, or mix of genetic types present. This would considerably complicate management of the resource. The ‘peripheral’ type of southern calamary may have a reproductive strategy more towards the terminal end of the spawning continuum (Pecl 2001), and may therefore require a different management strategy to the other multiple spawning type of calamary currently found in Tasmanian waters. Additionally, hybrids of the two types appear to be reproductively compromised (Triantafillos and Adams 2001), and so substantial mixing of the two types may lower the reproductive output of the population.
Ecologically, the importance of southern calamary should not be under-estimated. It is a major component in the diet of pilot whales and bottlenose dolphins (Gales and Pemberton 1992). Unspecified squid are also major prey items in Australian fur seals, Minke whale, southern right whale dolphin, killer whale and porpoise in Tasmania or southeast Australian continental shelf (Davenport and Bax 2002). All major predator groups (sharks, fishes and marine mammals) rely on squid populations as a significant component of their diet (Smale 1996). Conclusions? The potential impacts of climate change at the individual, population and fishery level discussed here for southern calamary in Tasmania have a much broader relevance than this specific species at this location. Inshore squid species with similar life–history characteristics, also targeted as part of multi-species artisanal fisheries, occur throughout the world on the northeast seaboard of North America, the Pacific coast of South America, the south coast of Africa, and small seaports along the European Atlantic and Mediterranean oceans. In temperate waters the next 100 years will see over 100 generations of these highly responsive creatures, in comparison to a handful of generations for sharks, tuna, or other larger predators of our oceans. Squids, and cephalopods in general, have the intrinsic flexibility to adapt to climate change - their life-history and physiological traits enable them to be opportunists in variable environments (Rodhouse and Nigmatullin 1996). Additionally, we will not have to wait decades to determine what these effects are. For species where we have established good baseline data, changes will be immediately obvious, generation by generation. In longer-lived predators it will however, take decades to establish cause and effect on their life-histories, populations and abundance. Whilst definite answers to our questions about ocean-scale climate change and the potential impacts on inshore squid population dynamics or fisheries biology are impossible, one thing is for certain, and that is that the pace of life for this high-speed group will increase even further. Directory: downloads downloads -> Northern England’s set-jetting locations downloads -> Dynatest 3031 lwd light Weight Deflectometer downloads -> Forth coming competitive exams downloads -> Brush High School Morning Announcements Friday, September 05, 2014 all school downloads -> Year 9 The Arts — Music downloads -> Years 7 and 8 standard elaborations — Australian Curriculum: Music draft downloads -> Chris Young sets 2016 “I’m Comin’ Over” Tour headlining dates downloads -> Slavery and Abolition: the Plymouth Connection Introduction downloads -> Summer Assignment Download 363.82 Kb. Share with your friends:
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