The potential effects of climate change on southern calamary in Tasmanian waters: biology, ecology and fisheries


(I) Southern calamary and the fishery in Tasmania



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(I) Southern calamary and the fishery in Tasmania

Southern calamary are a shallow water species, endemic to southern Australian and northern New Zealand waters. It is one of the most common cephalopods in the coastal waters of southern Australia, and is commercially harvested in Tasmania, South Australia, Victoria and New South Wales. In Tasmania, southern calamary are targeted as part of the multi-species Tasmanian Commercial Scalefish Fishery (TCSF) and are taken commercially along the north and east coasts of Tasmania and off Flinders Island, with the greatest proportion of the catch taken in the central east coast region (Great Oyster Bay and Mercury Passage) (Figure 1). The TCSF consists of a wide range of operator types, with calamary fishers falling under the category of what has been described as high market price ‘artisanal’ or ‘cottage’ type owner/operators using aluminium boats under 6 meters in length (Bradshaw 2003). In total, the TSCF engages around 150 full time fishers comprising approximately 400 people. The total catch for the 35 species targeted in the TSCF was 1,319.4 tons in 2001/02 (down from over 2,000 tons in the early 1990’s), with southern calamary the third highest component of around 103 tons (up from under 10 tons in the early 1990’s), or about 8% of the fishery (Lyle 2003).


Rising prices (from $4.50-$12 AUD) and expanding markets have led to dramatic increases in both catch and effort for southern calamary. Catch and effort have tripled in the last 5 years and there are concerns about sustaining such high levels of exploitation (Lyle, 2003, Figure 2). Management concerns have led to the introduction of short-term closures of the major spawning areas, ranging from rolling two-week closures to a three-month block closure. The southern calamary fishery in Tasmania is very small by international standards, most other inshore squid fisheries around the world are in the order of around 2,200-15,000 tons (Roberts et al. 1998). However, to the small population of Tasmania, and in particular the smaller coastal fishing towns on the east coast, it is considered very important (Bradshaw 2003).
Southern calamary are fished during the day over shallow areas of seagrass and macro algae (<10m depth) using a variety of methods including purse seine, beach seine, spear, and dip net, however, squid jigs on hand lines are the primary method (Lyle 2003). For the main part, the fishery targets spawning aggregations, and most of the spawning activity on the east coast of Tasmania is concentrated in Great Oyster Bay (Moltschaniwskyj and Pecl 2003), which is an area of convergence between warm, nutrient poor East Australian Current (EAC) water of sub-tropical origin and cool, nutrient rich water of sub-Antarctic origin (Harris et al. 1987).
Southern calamary are a fast growing, short-lived (<1 year) and multiple spawning inshore species although, as with all other loliginid squids, we have no information about the frequency of egg deposition or how many batches may be laid (Pecl 2001). Low levels of spawning take place throughout the year, however, there is a distinct observable peak in the austral spring and summer (Oct-Jan) when southern calamary aggregate over shallow inshore spawning grounds (Moltschaniwskyj and Pecl 2003). All life-history characteristics of southern calamary examined to date are highly variable, including, egg size and embryo mortality (Steer et al. 2002), annual egg production of populations (Moltschaniwskyj and Pecl 2003), hatchling size (Steer et al. 2003a), level of reproductive investment (Pecl 2001), and growth (Pecl in press).


(II) Climate change and southern calamary

The abiotic and biotic effects of ocean-scale climate change will have functional implications at the species, population, and ecosystem level. In this paper we take a ‘bottom-up’ approach, firstly examining how climate change may impact on the physiology of individuals, thereby altering their life-histories. We then discuss how these individual-level effects may be consequently expressed at the population-level.



(1) Individual effects


To examine potential effects of climate change at the individual level, we consider squid at several developmental stages as it is likely that environmental variables, temperature for example, will influence each life-history stage quite differently. We therefore deal with the following discrete developmental stages separately, A) embryonic development and hatching, B) post-hatching growth, and C) spawning adults.


(A) The embryonic and hatching phases


Mature southern calamary spawn large, individually encapsulated eggs, collective packaged in gelatinous material and forming strands of 3 to 9 eggs (Steer et al. 2003b). Strands are attached directly to seagrass, macro algae holdfasts, or embedded directly into the sand. Most commonly eggs are attached to Amphibolis seagrass, with many strands laid together to form egg mops of several to hundreds of strands (Moltschaniwskyj et al. 2003). The short life-span of squid means that the success of the next generation relies entirely on the capacity of each generation to produce viable offspring (Boyle and Boletzky 1996). For this reason alone, factors affecting the embryonic and juvenile phases will have crucial impacts on population success. Additionally, the embryonic phase of southern calamary is around 1-2 months (Steer et al. 2003b), and thus represents a significant portion of the entire life-span (10-12 months, Pecl in press).
As temperatures increase, development times of cephalopod eggs decrease (Boletzky 1994), provided that temperatures do not fall outside thermal tolerance boundaries (Gowland et al. 2002). However, although hatchlings emerge quicker under elevated temperatures, there is a negative relationship between incubation temperature and hatchling size (Vidal et al. 2002), so that the under warmer temperatures hatchlings emerge smaller (eg: Sepioteuthis australis, Steer et al. 2003a). Within a single spawning season, southern calamary hatchlings emerging at the start of the season (cooler) may be as large as 0.057g, whilst at the end of the spawning season (warmer) hatchlings may be as small as 0.023g – only 40% of the size of the cooler hatchlings (Pecl et al. in press a). Warming oceans may therefore see a downwards shift in the size of squid hatchlings emerging from inshore spawning grounds.

(B) Post-hatching growth


Smaller southern calamary hatchlings may mean smaller adults, or at least no net increase in size-at-age, even if growth rate is substantially elevated by temperature. The effect of temperature on the growth rate of individuals, providing food is not limited, is very clear - warmer temperatures will promote faster growth over shorter life-spans (see Forsythe in press). However, as growth in juvenile cephalopods is exponential, growth works like compound interest on an investment, and the starting size of the investment is crucial. For example, a 0.023g hatchling growing at 10% body weight per day would be 186g after three months, whereas a 0.057g hatchling growing at the same rate would be 462g after the same time period. If elevated temperatures reduced hatchling size to say, 0.01g, a hatchling of this size growing at 10% would only be 81g after three months! To maintain adult size-at-age under elevated temperatures, the 0.01g hatchling would have to grow at 11% to catch up to the 0.023g hatchling. Thus, the effects of elevated temperatures on the hatchling size and post-hatching growth rate will likely be opposing forces on the size at age of adult squid (see Figure 3).

Temperature driven changes in metabolic rate are directly coupled with feeding rate and growth rate (Forsythe 1993). Growth rate however, may increase or decrease depending on the nature of the food x metabolism x temperature relationship (Brett 1979). Not all species will grow faster under increased temperatures, as increased temperatures may decrease growth rate through either insufficient food supply, or reduced growth potential (see Jackson and Moltschaniwskyj 2001a). Some species that grow slower in warmer waters may be at their physiological limits with respect to temperature resulting in reduced growth rates (eg: Loliolus noctiluca Jackson and Moltschaniwskyj 2001b). With respect to growth of southern calamary, we know that:



  • Summer hatched grow faster than those hatched in winter (Pecl in press).

  • Warmer years may give rise to faster growing squid, although slow growers may still be present. Growth rate variance also appears greater in warm years (Pecl et al. in press b).

  • Life-history plasticity is sex-specific. Males vary more in size and growth, while females vary more in condition and level of reproductive investment (Pecl et al. in press b).



  • Southern calamary in warmer lower latitude populations (NSW, Australia) grow faster (Pecl 2000). Genetic differences between locations may also influence growth in Southern calamary (Triantafillos and Adams 2001, Triantafillos in press).and may also be more at the terminal end of the spawning continuum than Tasmanian southern calamary that are clearly multiple spawners (within a single extended season, Pecl 2001). HMM, NOT SURE HOW and where to fit in genetic type stuff



Thus, with respect to potential changes in growth rate of the Tasmanian population under a regime of elevated temperatures, several outcomes (not mutually exclusive) are possible.

Firstly, if individuals are able to obtain sufficient resources (both food and oxygen, see below) growth rates will increase (more so for males) as will variance in growth rate. However, adult size may not necessarily increase as hatchling size, the starting point, will decrease. Under continued temperature elevation, there will likely come a point where growth rates start to decrease as metabolic costs continue to escalate and growth potential is subsequently reduced.



Secondly, as a function of increased growth rate, it is very likely that the average life-span of squid will decrease (eg: Loliolus noctiluca Jackson and Moltschaniwskyj 2001b) and individuals will mature younger and at a smaller size (eg: Sepioteuthis lessoniana, Jackson and Moltschaniwskyj 2002).




Metabolic considerations – Owing to the high metabolic rates of squids, growth costs are likely to dominate energy flux through an individual cephalopod (Wells and Clarke 1996). In general, squid eat more and grow more rapidly than fish at comparable sizes and temperatures (Forsythe and Van Heukelem 1987). Gross growth efficiency is also exceptionally high for poikilotherms, estimated at between 20-30% for squid (O’Dor and Wells 1987). Feeding rates increase with temperature, however there is no empirical evidence that food conversion rates change detectably with temperature (Wells and Clarke 1996). Adult squid eat a large percentage of their body weight in food per day eg; Loligo opalescens 15-18% (Yang et al. 1986) and the much larger Dosidicus gigas 13.1% (Erhardt 1991). Hatchlings are even more voracious with Sepioteuthis lessoniana hatchlings for example consuming up to 72% of body weight in food per day (Segawa 1990). Failure to feed for even short periods is disastrous for animals with such high metabolic rates and low levels of metabolic reserves (Rodhouse and Nigmatullin 1996). The time period that new hatchlings can survive without food is also shorter at higher temperatures (eg: Dosidicus gigas, Ichii et al. 2002). Under a regime of elevated temperatures, smaller hatchlings would therefore need more food but have less time in which to find it before facing mortality. In this way, productivity changes may shift the temperatures defining thermal limits for species (Welch et al. 1998).


Responses to prey and productivity – Potential changes to the productivity of the world’s oceans are also of concern with respect to squid populations. This can be illustrated with the Loligo opalescens population off California. Jackson and Domeier (2003) demonstrated that although temperatures were much higher during the El Niño event, squid had slower growth rates and were strikingly smaller from lack of food due to drastically reduced productivity associated with a cessation of upwelling. When the environment changed to La Niña conditions with resumption of upwelling, increased productivity and abundant food, squid grew faster and much bigger due to the increased prey, despite cooler temperatures. Additionally, Piatkowski et al. (2002) reported that the biomass of cephalopods ingested by seals in Antarctica decreased during El Niño years, although this may have been caused by other factors and may not necessarily reflect reduced prey availability for the cephalopod populations.
Squid are trophic opportunists that can occupy broad trophic niches and exploit the temporal and spatial variability in prey populations. So although squid need vast quantities of prey, they have a greater trophic flexibility than most other groups and this may help them to still prosper during periods of reduced productivity. Squid can feed equally effectively on small macrozooplankton or on fish that may be larger than themselves (Rodhouse and Nigmatullin 1996). Many cephalopods are cannibalistic and southern calamary is no exception (Jackson and Pecl 2003). Indeed, from an individual perspective cannibalism may not be a bad option – Segawa (1990) found that growth of Sepioteuthis lessoniana hatchlings was greatest when fed conspecific hatchlings (compared with fish and mysids).
Physiological considerations – Experimental data has shown that oxygen consumption of squid increases linearly with body weight, while metabolism increases continuously in association with increases in temperature (Segawa 1995). This means that energetically, smaller squid do better at higher temperatures and large squid do better at lower temperatures (O’Dor and Wells, 1987). Many species show intra-school cannibalism, which may be an alternative to reducing metabolic rate when food is unavailable (O’Dor and Wells 1987). However, under a scenario of climate change, even if squid can obtain sufficient food (by either being such flexible trophic opportunists, or by eating each other) to maintain increased metabolism, will they be able to obtain sufficient oxygen to fuel metabolic requirements? Respiratory proteins are very sensitive to changes in pH, with large decreases in oxygen affinity as pH decreases. Climate change may result in a reduction in seawater pH due to elevated CO2 and this will result in a decreased ability to bind oxygen for transport to the tissues (Seibel and Fabry 2003). Such expected changes in ocean pH are sufficient to impair oxygen transport and limit scope for activity in energy-hungry squids (Seibel and Fabry 2003). This could impact individual squid via disturbances to acid-base balance, oxygen transport and metabolic processes, with cascading effects of growth, reproduction and survival (Seibel and Fabry 2003).




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