Spatial and temporal variations in female size at maturity of a Southern Rock Lobster (Jasus edwardsii) population: A likely response to climate change

Abstract

The size at which sexual maturity is reached is a key population parameter used to guide the setting of minimum legal size limits in fisheries. Understanding spatial and temporal variations in size at maturity is fundamental to management because the relationship between size at maturity and minimum legal size limits affects the fraction of the mature population biomass that is harvested, and resulting egg production, larval settlement and recruitment. This study measured the size at maturity of female Southern Rock Lobster (Jasus edwardsii) across South Australia between 1991 and 2015 in relation to known oceanographic characteristics, surface and subsurface temperature data, and relative changes in lobster abundance. There was pronounced north to south spatial variation in estimates of size at maturity. Larger average size at maturity was recorded in warmer north-western areas of the fishery relative to the cooler waters of the south-east. Estimates of size at maturity also differed over 25 years across the fishery. However, the nature of temporal responses varied spatially, and were more consistent with variations in surface and subsurface water temperature at local-scales than changes in lobster density. In the well-mixed waters of the north-western, western and south-eastern parts of the fishery, relatively high rates of increase in sea-surface temperature and size at maturity were recorded since 1991, indicating that size at maturity may be responding to ocean warming associated with global climate change. In more central parts of the fishery, contrasting temporal signals in sea-surface temperature (positive) and bottom temperature (negative) indicated increases in upwelling strength over the study period, and formation of a bottom cold pool below a warm surface layer, with corresponding decreases in size at maturity recorded. The spatio-temporal changes in size at maturity measured in this study highlight the need for oceanographic information to be integrated into future stock assessment models to enhance harvest strategy development, allow timely adaptive management decisions and increase the resilience of fisheries to the impacts of climate change.

Westward range expansion of the eastern rock lobster (Sagmariasus verreauxi) in Australia

“…However, while investigating temporal changes in size at sexual maturity in J. edwardsii , McLeay et al . (2019) highlighted high rates of increase in sea-surface temperature within South Australia since 1991. This suggests that local environmental conditions within South Australia are now favourable to eastern rock lobster settlement, survival, and maturity, to adult stages.…”

“…The normal temperature range of S. verreauxi in New South Wales is approximately 14.5-21.5 °C while that of southern rock lobster in south-eastern Australia tends to be cooler at approximately 9-21 °C (Holthuis, 1991). However, while investigating temporal changes in size at sexual maturity in J. edwardsii, McLeay et al (2019) highlighted high rates of increase in sea-surface temperature within South Australia since 1991. This suggests that local environmental conditions within South Australia are now favourable to eastern rock lobster settlement, survival, and maturity, to adult stages.…”

Puerulus settlement forecasting in a harvest strategy evaluation of the rock lobster fishery in South Australia

“…For example, marine heatwaves and ocean warming during 2006-2011 have caused recruitment declines in the Panulirus cygnus fishery in Western Australia (Caputi et al, 2019;de Lestang et al, 2015). Similarly, large-scale decreases in recruitment in the southern rock lobster fishery across south-eastern Australia in the 2000s resulted in simultaneous declines in fishery performance across South Australia, Victoria, and Tasmania (Linnane et al, 2019;Linnane, Gardner, et al, 2010) which appears linked to warming oceanic environments impacting lobster reproductive capacity (McLeay et al, 2019).…”

“…For example, marine heatwaves and ocean warming during 2006–2011 have caused recruitment declines in the Panulirus cygnus fishery in Western Australia (Caputi et al., 2019; de Lestang et al., 2015). Similarly, large‐scale decreases in recruitment in the southern rock lobster fishery across south‐eastern Australia in the 2000s resulted in simultaneous declines in fishery performance across South Australia, Victoria, and Tasmania (Linnane et al., 2019; Linnane, Gardner, et al., 2010) which appears linked to warming oceanic environments impacting lobster reproductive capacity (McLeay et al., 2019). Future effects of climate change on lobster recruitment are unknown, although past research and our findings highlight the need for ongoing recruitment monitoring of commercially important lobster fisheries, with conservative harvest strategies that react to recruitment declines.…”

Size at sexual maturity and seasonal reproductive activity of the Caribbean spiny lobster Panulirus argus

“…It is possible that there is a level of genetic adaptation in response to increased sea temperature where a smaller size at maturity is favorable (Le Bris et al 2017). The size at sexual maturity of the southern rock lobster Jasus edwardsii has also changed according to water temperature between 1991 and 2015 (McLeay et al 2019). Temperature is an important influence which mediates physiological factors that drive processes such as reproduction and growth (FAO/WECAFC 2018).…”