Recently I presented my project proposal to members of the marine biology department at my university. It was a pretty daunting thought, having to speak about what I would like to achieve this year, fully open to to all criticism…good or bad.
It went pretty well with my being able to answer most questions to the best of my ability, given the fact that I am certainly no expert on the topic and particular subject matter. I figured it would be good to share it on here and to document my progress as I continue to work on it…who knows maybe it will even boost my productivity.
The topic I have chosen to work on this year is to complete a Stock assessment of the Panga (Pterogumnus laniarius) found within the Agulhas Bank of South Africa.
Rationale/motivation for the project
With approximately two thirds of South Africa’s borders being coastal, the fishing industry plays a huge role to the GDP and economy, especially within local and rural communities. For this reason, it is vitally important that we ensure all fish stocks are being harvested sustainably, especially in light of exponential population growth and increased unemployment, so as to ensure that future generations have sufficient food security, employment and that biodiversity and ecosystem function is not compromised as a result.
The Panga, found along the Agulhas Bank of South Africa, is a slow growing species that reaches a maximum age of 16 years. Previous studies have calculated its total mortality, natural mortality and fishing mortality as 0.36 per year, 0.28 per year and 0.08 per year respectively. These fish exhibit a gonochoristic lifestyle with reproduction occurring throughout the year, peaking in winter. In its juvenile form they feed predominantly on mysids, they then move to feeding on brittle stars and amphipods when they are in their sub-adult stage. Once they reach adulthood they feed on larger prey, including crabs, polychaetes, brittle stars and fishes.
This species is the most abundantly caught seabream in SA. It is caught by inshore and offshore trawlers, commercial hand line and recreational hand line. It was most heavily fished by Japanese and Taiwanese trawlers in the 1960’s. Catches peaked between 1964 and 1966 when an average of 16 000 tons was harvested. From 1968 to 1972 catches declined after the establishment of the EEZ and implementation of a foreign quota whereby only 1700 were allowed to be caught per year. With the implementation of this legislation the Panga fishery declined, with most fish being caught in the horse mackerel fishery. In present day the species is caught predominantly as bycatch in the hake and horse mackerel directed fisheries. The small seabream is an important food fish among low income South Africans. Currently the species is not well managed and there are no quotas set in place. The sustainability of the fishery is therefore in question.
Attempts at fitting models to fishery data have been thwarted by a lack of resolution. Catches were never assigned to trawls, but rather reported at the level of the trip. I will attempt to calculate a CPUE index based on the trip level data, and together with total catch from all fleets fit a production model. The model will be compared to assessments based on survey CPUE data.
Appropriate targets will be considered and recommendations for suitable quotas over the next five years will be based on model outputs.
This project will use catch and catch per unit effort data from inshore (80-100m) trawlers over the last 32 years to fit a simple production model (glm). The trip level CPUE data will be standardised, using area, month/season, vessel and year as factors. To mitigate other factors affecting q, such as specific targeting we will be throwing out all data found on sole grounds as Panga are not found within that region. These are schooling fish with no stock structure and that will be taken into account as well.
The standardised CPUE series will be used as the abundance index. The catches from all fleets will be used as the catch. The model will estimate B and F and q, from which reference points (MSY) will be deduced.
The assessment will be compared with the assessment of Panga based on the survey data.Using both assessments, I will project the fishery forward and make recommendations on future precautionary catch limits.
So there it is in all its glory… my life for the next couple of months. Lets hope it all goes to plan 🙂
The biology of the panga, Pterogymnus laniarius (Teleostei: Sparidae), on the Agulhas Bank, South Africa. Authors: Anthony J. Booth & Colin D. Buxton