Here, I unravel the complex drivers influencing the population dynamics of an important sportfish, once heavily targeted on its spawning aggregations.

This research was supported with a QUEST grant awarded by NOAA Fisheries to B.X. Semmens. The following synopsis is taken from our manuscript, which is currently in revision for publication in Marine Ecology Progress Series.

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

Erica T. Jarvis Mason¹, Thomas V. Riecke², Lyall F. Bellquist^1,3, Daniel J. Pondella II⁴, Brice X. Semmens¹

¹Scripps Institution of Oceanography, University of California San Diego, California, USA
²Department of Ecosystem and Conservation Sciences, University of Montana, USA
³California Oceans Program, The Nature Conservancy, California, USA
⁴Vantuna Research Group, Occidental College, California, USA

Abstract

Aggregation-based fisheries are notorious for booms and busts driven by aggregation discovery and subsequent fishing-induced collapse. However, sporadic recruitment in some since-protected populations has prolonged 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 bespoke 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 indicate a history of multidecadal windows of fishing opportunity and fishing-induced collapse. The appearance of these windows in time appears largely driven by sporadic, warm water pulses, in which larvae may not be locally sourced. At present, traditional aggregations remain absent following a prolonged fishery collapse despite evidence of incipient population recovery. The lack of an associated fishery recovery suggests that harvest on spawning aggregations may have reduced densities enough to impact the behaviors driving aggregation dynamics. Aggregate spawner populations that are dependent on sporadic strong recruitment, especially those at their geographic margins, are thus highly susceptible to sudden and potentially extended periods of collapse, making them ill-suited to high CPUE fishing that occurs on spawning grounds. If the goal is to balance the protection of spawning aggregations with long-term fishery sustainability, then limiting aggregation-based fishing during spawning season may be the best insurance policy against collapse and recovery failure.