• Spatial variability in size at maturity and reproductive timing of golden king crab (Lithodes aequispinus) in Southeast Alaska

      Olson, Andrew P.; Eckert, Ginny L.; Kruse, Gordon H.; Siddon, Christopher E. (2016-08)
      Many crab fisheries around the world are managed by size, sex and season regulations, where male crabs are given at least one opportunity to reproduce before being harvested. Therefore, to set minimum legal size and fishing season for harvest, information on size at maturity and reproductive timing is needed. Lithodes aequispinus has supported a commercial fishery in Southeast Alaska since 1972, with an average annual harvest of 207 t. The current legal size and season for harvest are based L. aequispinus growth and maturity information from other parts of the range and limited information on reproduction. Additionally, evidence suggests that these life history parameters can vary spatially. Therefore, I investigated size at maturity, reproductive timing, and variation in harvest from the commercial fishery for L. aequispinus. I compared size at maturity estimates (males and females), mean spine contribution to legal size male crabs, and depth and bottom temperature among seven management areas in Southeast Alaska (Lynn Canal, Icy Strait, North Stephens Passage, Frederick Sound, Mid-Chatham Strait, Lower Chatham Strait, and Clarence Strait) and investigated reproductive timing of mature females in Frederick Sound. Male size of maturity estimates varied spatially, with an increasing trend with latitude and significant differences occurred among the majority of management areas. Female maturity estimates varied significantly among all areas, but showed no latitudinal pattern. The latitudinal pattern for size at male maturity in Southeast Alaska differed from published values in other parts of the range (Japan, Russia, the Bering Sea and from the Aleutian Islands to Canada), where size at maturity decreased with increasing latitude. When I investigated the ability of environmental factors to explain the patterns in Southeast Alaska, depth and temperature were not found to influence the spatial variation in male maturity estimates. Depth varied by management area, and males and females were distributed at similar depths. Temperature varied less than 1.0 °C among management areas, and monthly temperature measured at a mooring in the Gulf of Alaska also varied by less than 1.0 °C throughout the year at depths where L. aequispinus are found (250 m). Mean spine contribution to legal size varied spatially but did not influence calculated legal size. Reproductive timing was determined for eyed embryos, with projected hatching of embryos occurring from April to November, indicating that a distinct reproductive season does not exist. Management implications from this research are that the current legal size (177.8 mm/7.0 in carapace width (CW)) does not allow male crab to reproduce at least once before being harvested for all management areas. If legal size is increased to 196.5 mm/7.7 in CW, a higher proportion of male crab could reproduce at least once before being harvested. This size change could have negative economic impact to the commercial fishery with potential harvest lost in areas with smaller sizes at maturity. This study shows the importance of re-examining legal size and season based on an improved understanding of how life history characteristics change over space and the resulting implications for improved fisheries management.