Background
I am a graduate student at Simon Fraser University and Vancouver Island University and I am working to conserve rockfish.
Rockfish (Sebastes spp.) are a genus of scorpionfish that occur in the Northern Pacific. These fish are important mesopredators (not the top predator, but also not a feeder fish) in British Columbia’s ecosystem, and historically have supported a large fishery that targets them. We have driven these fish to the brink of disaster. Though we cannot be certain precisely how much we have drawn down their abundance, our best estimates suggest that some species have declined in numbers by as much as 90% over the past 30 years.
Rockfish are in this state because of overfishing. Rockfish are particularly vulnerable to overfishing for two main reasons. First, they have an extremely late age at maturity. It varies between species, but it can take anywhere from 10 to 35 years for rockfish to reach sexual maturity. That means it takes a long time to rebuild stocks after they are depleted. Second, they have highly variable recruitment success – one year, they may produce lots of offspring, while the next they may have next to none.
But not all fisheries are unsustainable. Here in British Columbia, the spot prawn (Pandalus platyceros) trap fishery is famous around the world for producing high quality product with minimal environ
mental damage. As opposed to tropical shrimp which are caught using highly destructive trawl nets or farmed at a cost of great environmental damage and human suffering, spot prawns are caught using small traps which inflict minimal habitat damage and have low bycatch.
There have, however, been reports that rockfish occur as bycatch in prawn traps. Rockfish are sensitive creatures – they have internal swim bladders that rupture when they are brought to the surface quickly. This barotrauma causes a great deal of damage to the animals, and most probably don’t survive being caught. Though the rate of bycatch is estimated to be low (0.004 rockfish per trap in the 2008 fishing season), when extrapolated across the entire fishery the potential exists for a non-trivial amount of rockfish mortality in this fishery.
It is important to keep this mortality in perspective. No matter how high the rockfish bycatch rate is, it is probably insignificant compared to the bycatch produced by trawlers or other fishing gear. In addition, only small juveniles are caught as bycatch, meaning that this fishery is not killing the big mature females that produce all the eggs to seed the next generation. There is also no habitat degradation due to trawling or farming that is characteristic of shrimp fishing elsewhere in the world.
However, with rockfish populations in such a precarious state, it is precautionary to reduce all sources of human-induced mortality as much as possible. Ideally, a technology should be developed that keeps the rockfish out while keeping the prawns in.
That’s where I come in.
What is PrawnCam?
In order to keep the rockfish out (or help them escape the prawn traps) we need to know what goes on during the time that the gear is underwater. This approach has been used in the design of bycatch reduction devices on trawl nets in tropical fisheries – start by strapping a camera to the rig and see what happens.
However, there are challenges to doing this with spot prawn traps. The traps are small, and are often deployed more than 100 meters underwater. At that depth, the pressure is more than 10 times greater than we experience at the surface, and there is little to no remaining sunlight. To make matters more difficult, prawn traps are deployed for a full 24 hours, making it difficult to find a system that can record for the entire duration at an appreciable frame rate.
PrawnCam is a purpose-built camera system that will record full 24 hour soaks of real prawn traps deployed in the wild where real fishermen might conduct their business. The goal is to gain an understanding of how and why rockfish are entering traps, in order to generate hypotheses about how to potentially redesign traps to keep the rockfish out. The secondary goal is to learn more about prawn fishing and the conditions that maximize prawn catch, which will further inform the design of the new trap (as it has to keep the prawns in while keeping rockfish out).
Over the next few weeks, I am going to post information about the progress of my study, including pictures from the deep and a guide explaining how I built the camera system. I am hoping that by doing this I will generate interest about the project and spark discussion about bycatch and bycatch reduction, and possibly reach potential donors who may be able to assist with the purchase of improved cameras, fuel for the research boat, and other incidental expenses.
Thank you for reading and I hope you enjoy this blog!
