Warning: This article contains several rather gross photos of fish dissections. If it’s any consolation I can assure you that they smelled even worse than they look.
A few weeks ago, I departed Las Cruces with two fisheries observers (Roberto and Kike) from the Pontificia Universidad Católica de Chile heading towards Patagonia. We were leaving to begin the first sampling session of the yellownose skate fishery stock assessment – a large multi-year project contracted by the Chilean government to uncover if this species is being sustainably managed or if changes in its regulation are required. I was incredibly excited to join this fieldwork, having completed the desk-based portion of the project involving a historical review of governmental data on the fishery. I was additionally excited to apply my new skills in elasmobranch ultrasonography from the conference in Argentina.
As this was the first fieldwork session for this project, I soon learnt that a fish stock assessment of this sort requires a lot of trial and error. The Chilean yellownose skate fishery is artisanal, meaning that it is performed by various small-scale/local operators. Each year the Chilean National Fisheries Authority (IFAP) announces the fishing season for this species and assigns catch quotas to specific regions. This creates a tricky situation for conducting a fish stock assessment as it means numerous small-scale actors are targeting the same resource in a short amount of time. It is not known exactly which boats, in which ports, and at what times will be fishing for skates as the quotas are designated on a region-wide basis. These factors mean it is essentially impossible to make a precise fieldwork plan. Our plan was to stop at various fishing ports where there are historical records of skate catches where we would hopefully find fishers targeting this species, allowing us to either sample their catch directly or to at least make a contact to plan future fieldwork sessions.
Across two days of driving, covering 1,500km, we stopped at various ports with little luck. When asking around nobody was fishing skates. Roberto and Kike let me know that oftentimes fishers in this region do not share information openly with government officials, fearing it will lead to a decrease in fishing quotas, harming their business. A much better strategy turned out to be visiting the homes of fishers that Roberto and Kike knew from previous projects, with whom they had built trusting partnerships. With their help, we were put in touch with fishers targeting skates. This experience showed me the unparalleled value of building trust and respect between fishers and researchers. Without their help, we would have been very unlikely to locate the necessary contacts to conduct the project.
Chiloé Island, Los Elefantes Processing Plant –
After two days of scoping out various locations and contacts we arrived on Chiloé island, the endpoint of our trip, where a definitive contact had been made with a fish processing plant receiving large quantities of skates.
Over the next week we spent every day at the processing plant, performing biological sampling of the yellownose skates before they were processed and packaged for export to the Korean market. We recorded standard biological sampling metrics for each individual such as total weight, total length, and the weight of various organs. Most importantly, every sample was assigned a maturity status (immature, maturing, mature) based on features of the claspers in males and of the gonads and ovaries in females. We also checked all female ovaries for the presence of egg capsules. The job was rather messy and smelly, involving long hours in the cold and the rain, but it was also incredibly exciting to see this species upfront and to learn the inner-workings of a fish processing plant.
Most specimens we assessed weighted 5-6kg and had a total length of around 95cm. However, one day a ship returned with skates weighting up to 90kg with lengths of 250cm! This made our sampling protocol tricky to follow, taking at least 3 people to move the fish onto the balance to weight them. It was established that for future fieldwork sessions a different system for dealing with such large specimens would have to be established.
Our sampling session ended unexpectedly when one morning we were informed that the quota for landing yellownose skates in the region had been filled. This was after only 2 weeks of fishing, showing the incredibly large pressure put on this resource due to its high exportation value. This situation yet again showed me that it is not always possible to make a precise fieldwork plan!
Data Processing and Unanswered Questions –
Upon logging all the collected measurements for the sampled specimens, and cross-referencing them with photos, several interesting factors important to address for the future of the project become apparent.
Firstly, all sampled males were classified as mature whilst sampled females were found across all maturity stages, including many immature females and even one individual carrying egg capsules. This suggests a difference in maturation timing and strategy between males and females. It is a concern to the sustainability of this stock if the fishery is capturing large proportions of females before they can produce eggs and to contribute to the replenishment of the population.
As concerning as this initial finding may be, the second realisation that we had is that the scale utilised for classifying the maturity stage for this species is likely inaccurate. In fact, the scale is based on other elasmobranch species, and the criteria on the scale were often vastly different from what we saw in the specimens. A revised maturity scaled, based on laboratory assessment of reproductive organs from this specific species is urgently needed to ensure that the maturity status fisheries observers are recording in the field accurately matches the biology of this species.
Thirdly, looking at the photos of the specimens and speaking with workers at the processing plant revealed that several skate species are being landed all under the name Yellownose skate. The five largest individuals we sampled were in fact most likely a different species (Raya espinosa) and should therefore be excluded from the analysis. The similarity of these two species and lack of clarity in their classification at fishing ports makes it likely that a misclassification of several species is also present in historical governmental data on this fishery.
Next Steps -
The next steps to progress this project involve addressing uncertainties in maturity scale and species classification – preparing better protocols for fisheries observers to follow in the upcoming fishing season (July-August). Without an accurate and standardized protocol sampling will not produce data which reflects the status of this fishery.
Being involved in this sampling season showed me how incredibly complicated it is to understand the status of a fish stock. Thinking about the fact that this must be done for every targeted species, across many years and timescales, has given me a newfound appreciation for everybody working in this field!
I come away with two main conclusions. Firstly, instead of rushing to collect as much data as possible on a fish stock it is crucial to ensure that the data being collected is scientifically accurate, as otherwise any statistical analysis will face the problem of ‘rubbish in, rubbish out’. Secondly, it is of paramount importance to establish good relationships between fisheries researchers and fishers for project success.
During my last week in Chile, I will be slowly traveling back up to the capital through Patagonia and the Chilean Lake District. For my final contribution to this project, I will be working to put together a report on changes in length-at-maturity data for the species in historical vs. newly collected data. The aim of this is to show whether the average size at which individuals of this species reach maturity has changed (an indicator of overfishing).
This is amazing work Marci!! I also just read your last post and both are so insightful. Excited to see where the project takes you next :)