Spatial variation in size at onset of maturity of female southern rock lobster <i>Jasus edwardsii</i> around Tasmania, Australia

Abstract

SUMMARY:The size at onset of maturity (SOM) of female Jasus edwardsii (Hutton, 1875) was estimated at 50 sites around Tasmania, Australia, based on the presence of ovigerous setae. There was a distinct spatial cline with the largest SOM being found at northwestern sites and the smallest at southwestern sites. Variation in SOM between sites was substantial and ranged from 59 mm to 112 mm carapace length. The observed decline in SOM from north to south was the reverse of that described for the same species at similar latitudes in New Zealand, which suggests that SOM in J. edwardsii is regulated by factors in addition to temperature. The effect of density on female SOM was investigated by comparing SOM estimates from two marine reserves with adjacent fished sites; however, there was no evidence of a decline in SOM with increasing density as predicted. A model of SOM predicted by latitude and longitude is described to facilitate spatial modelling of lobster stocks. The substantial and predictable spatial variation in SOM implies that management of this fishery would be improved by incorporating spatial elements, such as regional legal minimum size limits.Keywords: Jasus edwardsii; maturity; rock lobster; reproduction; spatial management. RESUMEN: VARIACIÓN ESPACIAL EN LA TALLA DE INICIO DE MADUREZ EN HEMBRAS DE LANGOSTA, JASUS EDWARDSII, ENTASMANIA, AUSTRALIA. -En 50 sitios alrededor de Tasmania (Australia) se estimó la talla de inicio de madurez sexual (SOM) en hembras de Jasus edwardsii (Hutton, 1875) basándose en la presencia de sedas ovígeras. La mayor SOM fue observada en la región del Noroeste y la talla menor en el Suroeste. La SOM varió entre 59 mm y 112 mm en longitud del caparazón. La disminución en la SOM desde el norte hacia sur fue inversa a la descrita previamente para la misma especie en similares latitudes en Nueva Zelanda. Esto sugeriría que la SOM en hembras de J. edwardsii es regulada por otros factores además de la temperatura. El efecto de la densidad de langostas en la SOM de hembras de J. edwardsii fue comparado usando SOM estimadas a partir de sitios con alta (reservas marinas) y baja densidad (sitios de pesca) de langostas. El incremento en la densidad no disminuyó la SOM como fue previamente predicho. Para mejorar y facilitar los modelos sobre los stocks de langostas, se describe un modelo para predecir la SOM que incorpora la latitud y la longitud como componentes espaciales. Dado que la SOM depende substancialmente y de manera predecible de las variaciones espaciales, el manejo de la pesquería de J. edwardsii podría ser mejorado con la incorporación de componentes espaciales a los planes de manejo, como por ejemplo establecer regionalmente un tamaño límite legal.Palabras clave: Jasus edwardsii, madurez, langosta, reproducción, gestión espacial.

Utility of a Collaborative At‐Sea Sampling Program (CASP) for the California Spiny Lobster Commercial Fishery: Catch Characteristics and Implications for Management

“…For example, egg-bearing lobsters as small as 53-mm CL have been reported off San Diego in the South region (Hovel and Neilson 2011;Hovel et al 2015), while the smallest SAM reported in the North Coast region (Palos Verdes) was about 63 mm (Lindbergh 1955). The variation in SAM may be due to differences in temperature, as numerous studies of other lobster, including spiny lobster, have documented an earlier onset of maturity in warmwater areas (Templeman 1936;Annala et al 1980;Little and Watson 2005;Gardner et al 2006). Unlike in the South, our calculations based on the CASP data suggest that egg production in the Northwest Islands is greatest in the legal fraction of the population, which is vulnerable to fishing and thus at greater risk of reduction in egg production.…”

Colour variation in the southern rock lobsterJasus edwardsiiand its economic impact on the commercial industry

“…The rapidity in depth transition in shell colour was variable between regions and around Tasmania, but had a weak latitudinal trend, in a similar pattern to that which occurs with depth range of red lobsters' growth rates and size at onset of female maturity across this region (McGarvey et al 1999;Gardner et al 2006). The latter is thought to be driven by differences in temperature, whereas the strong relationship we document between red shell coloration and depth appears to have a dietary basis, presumably because of changes in reef composition and in prey items with depth.…”

Fewer eggs from larger size limits: counterintuitive outcomes in a spatially heterogeneous fishery

“…For example, growth of 100 mm CL females varies from 1 mm per annum in the southwest to 14 mm per annum in the northwest . Likewise, the size at onset of maturity roughly doubles across a similar spatial range from 59 mm CL in the south to 112 mm CL in the north due to environmental differences rather than density or effects of fishing (Gardner et al, 2006). Spatial heterogeneity in the fleet is most pronounced with longitude due to prevailing winds with fishers willing to tolerate lower catch rates on the more protected and accessible east coast (Hamon et al, 2009).…”

“…Spatial differences in growth were modelled with length transition matrices fitted to an extensive tag-recapture dataset of over 50 000 recapture records McGarvey and Feenstra, 2001;Chandrapavan et al, 2010). Egg per recruit varied spatially because of differences in growth and also because of spatial variation in size at onset of maturity (Gardner et al, 2006), although fecundity at size was constant across regions (Green et al, 2009).…”