Size Does Matter: Model Selection of Shark Attack Case

Shark unprovoked attacks consist of fatal and non-fatal cases. Numerous cases have been reported involving shark species from Carcharhinus melanopterus with length of 145.5 cm to half-ton Carcharodon carcharias. Currently there are more (P < 0.05) unprovoked non-fatal cases with the average is 28.46 cases/shark species (95%CI: 3.86-53.1) than unprovoked fatal cases, which the average is 5.12 cases /shark species (95%CI: -0.075-10.3). Hence this paper seeks to select the best shark size model that correlates with the unprovoked fatal and non-fatal cases. The studied sharks consist of 24 shark species with the average length is 268.18 cm (95%CI: 230-306 cm) and the average weight is 225.42 kg (95%CI: 128-323 kg). Based on the model and as described by low values of AIC and the highest values of R2 and adjusted R2 , shark weight followed by combinations of shark weight and length produced unprovoked fatal and non-fatal cases best models. The model for explaining unprovoked fatal cases is the shark weight with high numbers of cases observed in large size shark (weight⁓fatal cases, AIC = 165.359, R2 = 0.72, Adj. R = 0.71). While for non-fatal cases, the best model is also the shark weight (weight⁓non fatal cases, AIC = 246.93, R2 = 0.63, Adj. R = 0.59).

Size Structure and Sex Ratio of Black Tip Reef Shark (Carcharhinus melanopterus) Landed in the TPI Paotere of Makassar City and TPI Beba of Takalar Regency, Province South Sulawesi

Carcharhinus melanopterus in the southern waters of the Makassar Strait is caught with bottom longlines and bottom gill nets as bycatch, caught throughout the year without any management arrangements. The research objective was to obtain information about the size structure and sex ratio of C. melanopterus in the southern waters of the Makassar Strait. The method used is a survey method. Sample measurements were carried out at TPI Paotere Makassar City and TPI Beba Takalar Regency, South Sulawesi Province from July to September 2020. Measurement of total body length (TL:cm) and determining the sex ratio were carried out directly in the field. The results of the study on 144 sample fish showed that the total length range for C. melanopterus landed at the Paotere TPI was the same as those landed at the Beba TPI at sizes between 58 - 135 cm TL with an average length of 91.18 ± 3.32 cm TL and sizes between 51 - 139 cm TL with an average length of 91.1±2.21 cm TL for both male and female sex, respectively.The comparison of C. melanopterus landed in the two fish landing sites was in a balanced state but the male sex was smaller than the female sex.The sex ratio of male and female C. melanopterus is balanced. Most (69.44%) female C. melanopterus caught were relatively young.

Relationship between the biomass of reef shark and fish in South Morotai Waters, North Maluku, Indonesia

Sofyan JF, Ambariyanto A, Suwartimah K, Toha AHA. 2020. Relationship between the biomass of reef shark and fish in South Morotai Waters, North Maluku, Indonesia. Biodiversitas 21: 5605-5613. This study aims to determine the biomass of reef shark and fish in South Morotai Waters in North Maluku, Indonesia. The Audible Stationary Count and Underwater Visual Census method were used to collect the data of reef sharks and fish. Seven and one site locations of coral reef and shark ecosystems were surveyed and, the data were analyzed using regression analysis to obtain a correlation between the variables. The three reef sharks found were Carcharhinus melanopterus, Triaenodon obesus, and Carcharhinus amblyrhynchos. Biomass estimation of reef sharks and fish ranged from 0.59 to 19.97 kg/ha and 30.95 kg/ha to 49.92 kg/ha, consisting of 8 families. In the area of aggregations, both species were found in 7 sites, and the population of reef shark amounted to 86.96 kg/ha and fish was around 55.705 kg/ha, consisting of 9 families. There was a positive relationship between the biomass of reef shark and fish in South Morotai waters, and the index of determination was 0.8043, showing that the biomass of reef shark was influenced by that of fish. These results indicated the importance of biomass in determining the functional composition and diversity of reef shark and fish.

Thermal tolerance and hypoxia tolerance are associated in blacktip reef shark (Carcharhinus melanopterus) neonates

ABSTRACTThermal dependence of growth and metabolism can influence thermal preference and tolerance in marine ectotherms, including threatened and data-deficient species. Here, we quantified the thermal dependence of physiological performance in neonates of a tropical shark species (blacktip reef shark, Carcharhinus melanopterus) from shallow, nearshore habitats. We measured minimum and maximum oxygen uptake rates (ṀO2), calculated aerobic scope, excess post-exercise oxygen consumption and recovery from exercise, and measured critical thermal maxima (CTmax), thermal safety margins, hypoxia tolerance, specific growth rates, body condition and food conversion efficiencies at two ecologically relevant acclimation temperatures (28 and 31°C). Owing to high post-exercise mortality, a third acclimation temperature (33°C) was not investigated further. Acclimation temperature did not affect ṀO2 or growth, but CTmax and hypoxia tolerance were greatest at 31°C and positively associated. We also quantified in vitro temperature (25, 30 and 35°C) and pH effects on haemoglobin–oxygen (Hb–O2) affinity of wild-caught, non-acclimated sharks. As expected, Hb–O2 affinity decreased with increasing temperatures, but pH effects observed at 30°C were absent at 25 and 35°C. Finally, we logged body temperatures of free-ranging sharks and determined that C. melanopterus neonates avoided 31°C in situ. We conclude that C. melanopterus neonates demonstrate minimal thermal dependence of whole-organism physiological performance across a seasonal temperature range and may use behaviour to avoid unfavourable environmental temperatures. The association between thermal tolerance and hypoxia tolerance suggests a common mechanism warranting further investigation. Future research should explore the consequences of ocean warming, especially in nearshore, tropical species.