Thesis title: Age estimates and Distribution of the deep water shark, Centroscyllium fabricii
The black dogfish, Centroscyllium fabricii (Reinhardt, 1825) is a deep water shark, abundant throughout Greenland waters. This species is a commonly occurring by-catch species in commercial fisheries targeting the northern shrimp (Pandalus borealis) and juvenile stages of Greenland halibut (Reinhardtius hippoglossoides). However, only little is known about its biology and life strategies.
Fundamental biological questions concerning the black dogfish in Greenland waters is addressed in this study. This includes estimation of age, description of the overall distribution in Greenland and determination of age and size at maturity. In addition to historical catch data, 424 black dogfish are caught in offshore waters of Greenland between June and September 2016. Dorsal fin spines are sampled for age estimation, while eye globes are analyzed for age validation throughout measurements of 14C, 13C, 15N and maturity stages are investigated to determine the age and size at maturity.
Using fin spine growth bands, I have provided the first age estimates for black dogfish. Based on radiocarbon dating, these estimates are however minimum estimates as the largest individuals appear to be more than 50 years old. The reason for this underestimation is unknown, but continued spine growth with length suggest it is linked with vanishingly-narrow growth bands in the layers of the fin spine or non-annual growth band deposition at older ages. Additional studies using more lengths for radiocarbon dating could shed further light on the accuracy of the age readings as could tagging studies.
The data on trawl catches clearly show the distributional limit of black dogfish in both East and West Greenland. These are well connected with the dominating current system around Greenland and the temperature preferences of black dogfish. Moreover, the depth preferences are clearly shown and illustrate that the black dogfish is vulnerable as a bycatch species in bottom trawl fisheries; especially those targeting Greenland halibut.