Another example of similar interaction cited by Heithaus et al. (2008)(2):
“Similarly, longline research in the tropical Pacific has shown that catch rates for 12 large pelagic predators (tuna, [espadon, marlin, etc….] and sharks) were divided by 10 between 1950 and 2000, while catches of pelagic rays (Dasyatis violacea) and other small mesoconsumers were multiplied by 10 or 100 during the same period (Ward & Myers, 2005). These studies suggest that mesoconsumer communities may react strongly to the decline of top predators and that these effects occur on large spatial and temporal scales. »
EwE modeling software (Ecopath with Ecosim) has been widely used to explore the potential effects of shark decline, particularly on fish populations, in part due to the paucity of empirical data on fisheries-induced changes in fish populations. In this context, Ferretti et al. (2010)(3) report: “ [….] the effects of shark capture depend on the species involved and the ecosystem context (Stevens et al. 2000). Significant effects were observed especially for large sharks in coastal environments. For example, in French Frigate Shoals (Northwest Islands of Hawaii), a simulated decline in tiger sharks led to an increase in a variety of prey species, including seabirds, turtles, monk seals and reef sharks, leading to a rapid decline in tuna and trevally. [….] In a similar model from the island of Floreana (Galapagos), the disappearance of all sharks led to an increase in the abundance of toothed whales, sea lions and non-commercial reef predators, which forced a decrease in a number of commercial reef fish. and increase in small invertebrates through a four-layer trophic cascade (Okey et al. 2004). »
They also recall the consequences of the destruction of great sharks by net fishing programs created to protect South Africa’s beaches:
“The 50-year-old shark net program along the coast of KwaZulu-Natal in South Africa provides another good example of the potential ripple effects. From 1956 to 1976, while CPUEs [captures par unité d’effort] The decline of large sharks in net-fishing programs, recreational fishing derbies revealed a proliferation of small elasmobranchs in coastal waters and a decline in bony fish (Van der Elst 1979). The increase in small sharks was dominated by two species: juvenile Carcharhinus obscurus and Rhizoprionodon acutus. The latter were only slightly affected by shark nets, but were preyed upon by larger sharks. [….] Van der Elst (1979) proposed that the increase in these mesopredators contributed to the observed decline in bony fish, which constitute a large part of their diet. Independent projections estimated that between 419,000 and 2.8 million small sharks and ~5,000 dolphins escaped shark predation during the period 1956-1976 (Van der Elst 1979; Dudley & Cliff 1993). »
However, the ecological and economic consequences of the slaughter programs implemented by the mayor were NEVER studied. In Reunion, we kill the blind!
In 2012, the then chairman of the Fisheries Commission became famous with an irrevocable response: “Sharks suck, they eat all our fish!” “. A vision oh what obtuse, and completely disconnected from ecological reality.
Small local fishermen complain about fishing less and less and no longer see fishing as a profession with a future. But can we seriously think that we can eliminate the great predators of the ocean with impunity?!
(1) Myers R., Baum J., Shepherd T., Powers S., Peterson C. (2007) – Cascade effects of the loss of predatory Apex sharks from a coastal ocean. Science (New York, NY), 315, 1846-1850. HYPERLINK “https://www.science.org/doi/10.1126/science.1138657” https://www.science.org/doi/10.1126/science.1138657
(2) Heithaus MR, Frid A., Wirsing AJ, Worm B. (2008) – Predicting the ecological consequences of the decline of marine top predators. Trends in Ecology & Evolution, Volume 23, Issue 4, Pages 202-210, ISSN 0169-5347, HYPERLINK “https://doi.org/10.1016/j.tree.2008.01.003” https://doi.org/ 10.1016/j.tree.2008.01.003
(3) Ferretti F., Britten BW, GL, Heithaus MR, Lotze HK (2010) – Ecosystem patterns and consequences of shark decline in the ocean. Ecology Letters, 13: 1055-1071. HYPERLINK “https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1461-0248.2010.01489.x ” https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1461-0248.2010. 01489.x