USA Sharks Recovering!
Updated: Apr 26, 2021
In the United States, shark stocks were decimated between the mid-1970s and early-1990s - as much as 60%–99% reduction for some species. This was as a result of dwindling commercial fish stocks, which redirected the fisheries industry towards targeting sharks and because recreational shark fishing became popular after the release of Jaws in 1975. However, a shark fishery management plan (FMP) was established by the National Marine Fishery Service (NMFS) in the USA in 1993, in order to tackle these horrifying declines. This sought to regulate commercial and recreational shark fishing in federal Atlantic Waters. And there may be some good news today... it appears that certain shark populations in the USA may be recovering!
A recent study sought to assess how well the southeastern USA FMP was working. Using multiple data sources (including longline survey, drum-line survey, trawl survey and gillnet survey data), scientists modelled whether coastal shark populations had shown any signs of recovery since implementation of the FMP. This involved looking at their "relative abundances", meaning they considered how their abundances had changed over time relative to the first known population size.
They assessed the populations of several large coastal sharks: the sandbar shark (Carcharhinus plumbeus), the blacktip shark (C. limbatus), spinner shark (C. brevipinna) and the tiger shark (Galeocerdo cuvier), and also three small shark species: the blacknose shark (C. acronotus), sharpnose shark (Rhizoprionodon terraenovae) and bonnethead (Sphyrna tiburo) (Peterson et al, 2017).
Amazingly, the researchers reported positive findings! They found that, not only was every species showing increases in relative abundance, but that the abundance of the tiger shark had increased by 3% and the abundance of the spinner shark had increased by as much as 14%! This study can give us hope that protective measures can result in the recovery of shark populations (Peterson et al, 2017).
However, the researchers had several recommendations for how to implement successful legislation in the future:
Species-Specific Protective Measures
Firstly, the authors noted that, whilst the populations of all species were increasing, there were differences in how rapidly each species was able to recover after protection. For example, the tiger shark was able to recover so successfully due to their high "fecundity"; a single female tiger shark is able to produce an average of 41 pups every two years in the Atlantic. Species with lower fecundity were not able to increase so dramatically. Generally, the populations of larger coastal shark species remained depressed initially after implementation of the FMP, whilst smaller species which had younger age-of-maturity, were able to bounce back more quickly (Peterson et al, 2017).
Limitations on Selective Extraction
The authors also advised that selective extraction of certain portions of the population, can limit recovery after the implementation of protective measures. Many species of sharks segregate by size and/or sex, with males and females occupying different habitats, and neonate and juvenile animals living in an entirely separate area from the adult animals, in "nursery habitats". Therefore, certain life-stages are often extracted in disproportionally high frequency by fisheries, as the area the fisheries target contains one particular group or the fisheries may be limited in which individuals they may extract based on size (Peterson et al, 2017).
For example, the scientists hypothesised that the slow recovery of the sandbar shark was caused by fisheries' targeting juvenile animals prior to the implementation of the FMP. Upon protection, there was a lag in sandbar recovery because recruitment into the adult population was low, limiting further reproduction (Peterson et al, 2017).
Large-Scale Management Plans
Whatsmore, the researchers also noted that the increases recorded for the bonnethead and the Atlantic sharpnose shark were regional and that the increase of spinner shark abundance was actually very gradual. They hypothesised that, because multiple different management measures had been implemented for their protection, population recovery in these species was variable by area (Peterson et al, 2017).
In conclusion, the researchers stated that they suspected that the decrease in shark landings in fisheries globally over recent years, is unlikely to be due to the implementation of protective measures, but due to global reductions in shark abundances. They were hopeful that there were signs of recovery in the USA Atlantic coastal shark stocks, but suggested that, in order to implement successful protective measures, it will be important to consider the effects of both federal and state management regulations in the USA (Peterson et al, 2017).