Contrasting capture methods and health indicators among juvenile sharks in the nursery area of Boa Vista, Cabo Verde

Abstract

Stress levels in neonate and juvenile sharks can influence the health and survival of the individual, as well as the overall population resilience. This thesis explores interspecific differences in health and stress indicators in juvenile sharks caught in Sal Rei Bay (SRB), a multi-specific shark nursery area in Boa Vista Island, Cabo Verde. Body condition, capture resilience, and a range of biochemical parameters (cholesterol, glucose, phosphate, creatine, alanine aminotransferase, alkaline phosphatase, potassium, total protein) were assessed in four shark species frequenting SRB — milk shark (Rhizoprionodon acutus), blacktip shark (Carcharhinus limbatus), scalloped hammerhead shark (Sphyrna lewini), and Atlantic weasel shark (Paragaleus pectoralis) — caught using artisanal fishing methods traditionally employed in the region (gillnets and angling). Recuperation scores varied among species and generally indicated faster recovery in individuals captured by angling compared to gillnets. Milk sharks, however, tended to recover quicker after gillnet capture. Hammerhead sharks showed the overall slowest recovery. Significant species-specific differences were revealed in nearly all analysed indicators, with a frequent influence of the umbilical scar. A significant influence of gear type was only detected for the two biomarkers alanine aminotransferase and alkaline phosphatase. The present results showcase the influence of species, development, and fishing-method on physiological indicators in juvenile sharks in SRB, discussing how species-specific ecological and behavioural characteristics might have influenced the results obtained. The influence of environmental and other anthropogenic pressures should be considered more thoroughly in future studies. By yielding the first fundamental insights into the interspecific differences in stress levels among juvenile sharks in the SRB nursery area, the present dissertation contributes to the design of future and ongoing monitoring efforts. Further, it enhances the comprehension of local interactions between sharks and the local artisanal fishery, addressing a knowledge gap for formulating effective, locally-tailored conservation strategies.