Over the past few days, I had the pleasure of attending a workshop on the use of ultrasonography as a tool for assessing health and reproductive status within elasmobranch species. This workshop was hosted in the town of San Clemente Del Tuyu, Argentina and brought together fisheries experts and veterinarians from Chile, Argentina, and Uruguay.
I attended the conference with a team of fisheries observers from Chile with the objective of learning how ultrasonography can be used to assess the reproductive stage of female rays. Within Chilean fish stock assessments fish are generally categorized into one of two categories (immature and mature). A mature individual is defined as one which is capable of reproduction. This is an incredibly important feature for understanding the sustainability of a fishery, as if fishers are landing high levels of immature individuals this signifies that a large proportion of the population is being fished before reproducing and contributing to the replenishment of the population, signifying the likely occurrence of overfishing and a need for changes in fisheries regulations such as raising the minimum allowable catch size.
Within male elasmobranchs maturity status is identified through the size and calcification of claspers whilst in females by the development of the gonads and ovary, specifically the presence/absence of developed follicles within the gonads. Maturity in male elasmobranchs can be identified externally through a simple visual assessment of an individual. This means that fisheries observers can study the maturity of male elasmobranchs without a need for purchasing them from fishers, as the individual fish remain untouched and can therefore be sold by fishers. However, to examine the presence/absence of follicles within females a dissection is traditionally required, and thus each female individual assessed must be purchased. This is a tricky factor for this particular fish stock assessment, as each individual landed yellownose skate in the south of Chile can cost up to $70-$80. For a scientifically accurate assessment of this species thousands of individuals need to be sampled across several years, making the costs of this assessment incredibly high and potentially leading to limited sampling due to a lack of funding.
It is hoped that with ultrasonography fisheries observers can assess the reproductive status of female yellownose skates without the need for dissection. If this method proves successful, they will not need to purchase an individual to assess its maturity, allowing fishers to export their catch to their regular markets whilst a scientifically robust fish stock assessment is still carried out. This methodology could therefore greatly increase the sample size of females within this fish stock assessment, therefore providing a more accurate understanding of the status of the population and sustainability of current fishing practices.
Throughout the workshop, with the expertise of the veterinarians, I was able to learn how to operate the ultrasonography machine and to identify reproductive organs and assign them a maturity status within females of several elasmobranch species. Next week I am heading to Chilean Patagonia to test whether this methodology can be applied in practice to the yellownose skate across various fisheries landing ports.
Ahh this is incredible!! Super cool and exciting :)