Recruitment limitation increases susceptibility to fishing-induced collapse in a spawning aggregation fishery

Abstract

Spawning aggregation-based fisheries are notorious for booms and busts driven by aggregation discovery and subsequent fishing-induced collapse. However, environment-driven sporadic recruitment in some since-protected populations has delayed recovery, suggesting recruitment-limitation may be a key driver of their population dynamics and fishery recovery potential. To glean insight into this dynamic, we focused on an overexploited temperate aggregate spawner, barred sand bass Paralabrax nebulifer, and leveraged a long-term mark-recapture data set spanning different oceanographic and harvest histories in a custom Bayesian capture-mark-reencounter modeling framework. We coupled this demographic analysis with long-term trends in sea surface temperature, harvest, adult and juvenile densities, and historical accounts in the literature. Our results point to a history of multidecadal windows of fishing opportunity and fishing-induced collapse largely driven by sporadic, warm-water recruitment events, in which recruits may be externally sourced and local recruitment is negatively influenced by harvest. Following the last collapse, recruitment remained elevated due to novel, anomalously warm conditions. Despite signs of incipient population recovery, spawning aggregations remain absent, indicating that other potential factors (e.g. continued fishing during spawning season, Allee effects) have delayed fishery recovery to date. Recruitment-limited aggregate spawner populations, especially those at their geographic margins, are highly susceptible to sudden and potentially extended periods of collapse, making them ill-suited to high catch-per-unit-effort fishing that occurs on spawning grounds. If the goal is to balance protecting spawning aggregations with long-term fishery sustainability, then limiting aggregation-based fishing during the spawning season is likely the best insurance policy against collapse and recovery failure.