Documenting recovery of a spawning aggregation through size frequency analysis from underwater laser calipers measurements

作者：Heppell Scott A; Semmens Brice X; Archer Stephanie K; Pattengill Semmens Christy V; Bush Philippe G; McCoy Croy M; Heppell Selina S; Johnson Bradley C

来源：Biological Conservation, 2012, 155: 119-127.

DOI：10.1016/j.biocon.2012.06.002

• Population recovery
• Monitoring
• Marine protected area
• Nassau grouper
• Length analysis
• Length distribution
• Spawning aggregation

Many spawning aggregations of marine fishes have been fished beyond the point of sustainability, leading to increased calls for protection through seasonal and/or site-specific fishery closures. Once a closure has been put in place, monitoring the aggregation is imperative in order to learn whether protection leads to the recovery of the population. Current methods for monitoring the status of spawning aggregations rely largely on counts, either subsample or census, usually combined with capturing a subset of the fish to assess individual traits such as length and weight. Handling fish during the spawning aggregation can be stressful for the fish, and can ultimately lead to decreased spawning success, increased susceptibility to predators, or increased mortality through capture trauma or infection. Here we present a novel analysis for monitoring fish on a spawning aggregation that does not require the capture and handling of fish. Following a recovering aggregation of Nassau grouper (Epinephelus striatus) over seven spawning seasons, we show that length-distribution data can be collected by divers using a video-based system with parallel lasers calibrated to a specific distance apart, and subsequently use those data to monitor changes in the size distribution over time. We detected recruitment of new fish to the grouper spawning aggregation in the fourth year of monitoring. In addition to tracking size distribution trends over time, the length distribution information could be combined with an established length-weight regression and an estimate of total abundance to estimate spawning stock biomass. We qualitatively cross-validate this method with census data to evaluate its effectiveness in monitoring the recovery or decline of aggregating species that can be visually observed.

• 出版日期2012-10