Prior to the study, scientists and fishermen alike believed there could be an abundance of nephrops in an area where commercial nephrops fisheries have not previously taken place. This led to scientists from the food research institute Nofima and the Institute of Marine Research undertaking a study of the possibility of combining fishing for live cod and nephrops in Skagerrak and the North Sea.
We saw quickly that net-caught cod had problems getting rid of gas from the swim bladder and were more exhausted than fish caught with other gear, says Project Manager and Nofima Senior Scientist Kjell . Midling. Even though much of the fish was still alive and showed little sign of damage, the proportion of floaters and the stress levels were too high for the cod to be suitable for capture-based aquaculture.
However, a joint operation between cod fishermen with gill-nets and pot-fisheries for live nephrops is a potential that can lead to the fishermen in Skagerrak and the North Sea having more than one string to their bows. This area of sea has many shipwrecks, so called artificial reefs, which attract a large abundance of fish. Consequently, the gill-net fishery has developed many adaptations to take into account the special challenges the area poses. The fishermen set their nets round the wrecks at times of the day that are favourable in relation to scavenging amphipods and isopod species, which are a problem in the North Sea. As a result, the fishermen would have time to tend to other fishing gear, such as nephrops pots.
Learning from Sweden, Denmark and Scotland
Swedish fishermen in particular practice pot fisheries for nephrops, and there is also commercial activity in Scotland and Denmark. In Norway, nephrops is classed as a little utilized resource (LUR). However, combining gill-net fisheries and pot fisheries requires special rigging and is more labour-intensive than pure gill-net fisheries. Therefore, the primary goal of the project was to study whether it is possible to increase profitability by combining gill-net fisheries for live cod and pot fisheries for nephrops in the North Sea.
The Skagerrak Coast has long traditions involving the transport and storage of live seafood. The most important fishing gear has been hand lines, fish pots, Danish seines and trammel nets. Trammel nets have traditionally been utilized for live cod fisheries, as this net type is gentler. However, this project utilized ordinary nets. In Norway, nets are the fishing gear that lands the most cod.
Nephrops catches can be multiplied
Nephrops has been of increasingly larger importance in the fisheries in Southern Norway, but is still small in comparison to our neighbours. The annual global catch is currently approximately 70,000 tonnes. Scotland is unquestionably the largest actor, accounting for around 40,000 tonnes. The quality of the nephrops can deteriorate rapidly once it is caught and so it is important that it is landed in an undamaged and live condition. Consequently, pot fisheries are preferable, as this gear type offers better opportunities to deliver live and undamaged nephrops.
Several pot types were tested and two-chamber pots, which were originally developed for fish, captured nearly twice the number of nephrops as ordinary nephrops pots, says Midling.
However, the advantage of larger catches in the two-chamber pots was counterbalanced by the fact that some of the nephrops were damaged as a result of their claws getting stuck in the net and consequently it took a long time to tend each pot.
The scientists also established that there were large seasonal variations in the composition and volume of the catch. In October the capture rate when the pots were left for a 24-hour period was 14 times higher than in June, but the nephrops captured in June were larger than those in October.
Possible to transport live
Given the correct storage and chilling before packaging and export, nephrops can be transported for at least 27 hours without mortality.
Renewed interest in live capture of nephrops
The results point to the fact that there are large areas with nephrops stocks in the North Sea and Skagerrak where there is currently no commercial nephrops fisheries. These areas either contain shipwrecks or are so undulating that trawling for nephrops would not be a viable possibility. Planning is now underway for a Nordic collaboration to develop these trawling grounds into pure nephrops fisheries based on pots and live sales to high paying markets.
Our trial has led to increased interest along the Norwegian coast, also with respect to introducing pots in fishing grounds that currently utilize nephrops trawls, says Midling.