Abstract
The lack of long-term monitoring programs makes it difficult to assess signs of population recovery in collapsed marine populations. Fishery-induced changes in the life history of exploited marine fishes, such as truncated size and age structure, local extirpations, reductions in age at maturity, and changes in mortality patterns, have occurred. In the present study, we explored life history aspects of totoaba Totoaba macdonaldi, almost 40 yr after a population collapse, to examine whether totoaba maintained their life history pattern and to identify the potential threats of using fishing gear (hooks, gillnets). The results of the present study indicate that the totoaba size structure was not truncated as expected in overexploited populations; indeed, it was similar to that observed in the past. Totoaba have maintained their known historical distribution range. The spatial size structure and temporal distribution followed the known migration patterns of Total and natural mortality were similar. Contrary to recommendations for sustainable fisheries, caught fish contained a large number of juveniles, irrespective of method used. We conclude that the general life history (size structure, distribution, migration, and mortality) has not changed since the fishery collapse. However, the choice of fishing gear could compromise a positive recovery trend of the population. Moreover, poaching is a major ongoing threat to the recovery of totoaba.
Highlights
Successful species conservation involves more than preventing extinction; it includes the recovery of threatened species
(1) What is the size structure of the population? (2) Are totoaba still conserving their known spatial distribution range and migration pattern? (3) What is the spatial size structure? (4) What is the potential impact of hook and gillnet use on the population size structure? We aim to identify if the present-day totoaba population has recovered from its population collapse 40 yr ago, or whether it still shows signs of overexploitation, such as truncated population size structure, contracted species distribution range, changes in migration patterns, and mortality rates
Large and smaller totoaba were observed in the Core Zone near the Colorado River delta, which consisted of a single modal size group (1375 ± 114 mm; Fig. 3a)
Summary
Successful species conservation involves more than preventing extinction; it includes the recovery of threatened species. The fishing industry induces changes in the overall life history of marine fish, such as a reduction in the age and size structure, age at maturity, fecundity, and genetic diversity, as well as an increase in the potential for local extinctions (Dulvy et al 2003, Hoarau et al 2005, Enberg et al 2009, Heino et al 2013). Measuring these changes is useful to detect signs of population recovery (Abbitt & Scott 2001, Lotze et al 2011) in the absence of long-term information
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