Why do blacktip sharks die young in the Gulf of Mexico?



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Why do blacktip sharks die young in the Gulf of Mexico?

Blacktip sharks are regularly caught by coastal fishing vessels in Thailand and India, but they are not a desirable commercial target. The meat, sold fresh, frozen and dried and salted, is used by man, as well as liver oil and fins, used for the preparation of the famous shark fin soup.

They are also often used as bait for other fish. The IUCN Red List of the International Union for Conservation of Nature classified this species as vulnerable in 2020. In the previous assessment in 2009 it had classified it as close to the threat of extinction.

The populations of this species have experienced sharp reductions in some areas as a result of unregulated fishing. The reproduction rate of C. melanopterus is low, and therefore the possibility of recovery from these reductions is limited.

Added to this is the effect that coastal water pollution and climate change have on the habitat of this species.
Even in a portion of the Gulf of Mexico, these sharks face a dire fate. Research Grow fast, die young: Does compensatory growth reduce survival of juvenile blacktip sharks (Carcharhinus limbatus) in the western Gulf of Mexico? published on the Ecology and evolution, highlights various issues.

The researchers explain: "Effective conservation and management necessitate an understanding of the ecological mechanisms that shape species life histories in order to predict how variability in natural and anthropogenic impacts will alter growth rates, recruitment, and survival.

Among these mechanisms, the interaction between parturition timing and prey availability frequently influences offspring success, particularly when postnatal care is absent. Here, we assess how parturition timing and nursery conditions, including prey abundance and environmental conditions, influence the growth and potential survival of blacktip sharks (Carcharhinus limbatus) in western Gulf of Mexico (GOM) estuaries over their first year.

Catch data from long-term gillnet monitoring allowed for clear delineation of cohorts based on size frequency distribution plots, and showed that late parturition cohorts born in estuaries with fewer prey resources exhibited more rapid growth than early parturition cohorts that experienced more abundant prey.

Compensatory behaviors that promoted accelerated growth led to reduced second year residency, likely due to reduced survival resultant from greater risk taking and potentially due to reduced site fidelity attributed to larger body size.

Water temperatures influenced blacktip growth rates through physiological increases in metabolism and potential premigratory foraging cues associated with cooling temperatures. Gradual warming of the GOM (0.03°C year-1) was also correlated with earlier parturition across the study period (1982-2017), similar to other migratory species.

Considering current trends in climate and associated phenological shifts in many animals, testing hypotheses assessing compensatory growth-risk trade-offs is important moving forward to predict changes in life histories and associated recruitment in concert with current and future conservation actions, like wildlife management."