Compensation potential in six depleted groundfish stocks from the Northwest Atlantic

Abstract

Compensatory responses are important because they increase spawning stock biomass (SSB) growth rates in depleted fish populations. We analyze recruits per spawner (R/SSB) and spawners per recruit (SSB/R) data from six well-studied depleted, or depleted and recovering, Northwest Atlantic groundfish stocks for evidence of compensatory responses. All stocks had periods of high R/SSB at low SSB; however, R/SSB showed considerable variability, and significant compensatory responses were only found in two stocks. For compensation in SSB/R, relationships were significant for three of the stocks. We examined the potential impact of compensation in R/SSB and SSB/R on SSB growth rate and concluded that SSB/R could have a greater potential impact on enhancing SSB growth rate in depleted stocks. Overall, cod (Gadus morhua) populations showed greater compensation than flatfish, mainly due to the lower potential in flatfish to increase SSB/R. This suggests that cod are more resilient to overfishing than are flatfish. Estimates of population growth rate at low stock size, which ignore compensation in SSB/R, will underestimate maximum SSB growth rates. Compensation in both R/SSB and SSB/R should both be considered when evaluating stock productivity, sustainable harvest levels, and biological reference points.