| 英文摘要 |
The jumbo (or Humboldt) squid, Dosidicus gigas, is a large pelagic ommastrephid squid which distributed in the Eastern Pacific Ocean (EPO). The jumbo squid is an important component of its ecosystem in the EPO and is the main target of squid fisheries in this region. The central challenge for fisheries ecology is to understand the abundance variations of resources under fishing pressure and its synergistic effects to the ecosystems. The jumbo squid fishery in Taiwan is not dominant in context of production or values, while it could act as a substitute for Illex argentious fishery. Also, jumbo squid has been a target species of SPRFMO which enter into force on 23 September 2012. Therefore, it is essential to understand its population dynamics, environmental influences and fisheries management. This study applied fisheries data of D. gigas fishery in Taiwan to explore the variation of stock abundance and the environmental influences. The distribution of D. gigas abundance was higher in the coastal waters off northern Peru. The size composition harvested by Taiwanese fleet was identified as large-size group in recent years. The results of GAM showed the temporal and spatial variables could explain higher variation of squid abundance than other variables. This may result from highly variable features of squid populations and high migration pattern of jumbo squid. A decreasing trend of squid abundance index was found since 2005 afterward. The average annual proportional escapement in 2002~2012, which estimated by depletion method, was 52% which higher than the management target (40%) suggested in the Illex fishery. The annual spatial patterns of fishery in recent years were different from the earlier years (before 2007) which may imply a change in migration pattern for the jumbo squid, or a potential change in the environmental conditions of habitat. Designing and collecting biological data, and including more environmental variables in models may improve our understanding to variability of abundance for jumbo squid in the EPO. |
