ANSWER 1

Blue swimmer crab (BSC) are a relatively short-lived species (3-4 years maximum life span) who’s biology and population dynamics are closely related to environmental conditions. In particular, levels of recruitment (the number of juveniles entering the population) can substantially vary from year to year with changes in environmental conditions. Water temperature has been shown to influence the growth rate, size at maturity, timing of spawning and fecundity (number of eggs produced each year) of adult crabs, as well as the number of eggs and larvae that successfully develop into juvenile crabs. Other ecosystem changes, such as increase or decreases in primary productivity, can also have major impacts on local crab populations.

BSC are a warm water associated species that typically occur in estuaries and nearshore marine waters where water temperatures range 18-26 °C and salinities are marine or close to that of full-strength seawater (\~35). Temperatures outside of this range can negatively impact on spawning and recruitment, and in extreme cases cause mortality and/or stock collapses. Likewise, very fresh or hypersaline conditions can have negative effects on crab stocks.

Environmental changes in recent decades have been linked with substantial BSC stock declines in several areas along the west coast of WA (e.g. Shark Bay and Cockburn Sound). However, on the flip side, there has been an increase in BSC catches along the south coast of WA in waters which have historically been too cold to support BSC populations. Decreased rainfall and rising sea levels may also have a positive effect on crab stocks in some estuaries due to increased marine-like conditions for longer throughout the year and over a larger spatial area, and therefore greater available habitat for BSC.