Tagging studies at the end of the 1950s showed that the stock migrated from a summer area by Scotland and a winter area in Norwegian waters. Similar tagging studies in the 1970s showed a more southern distribution. In recent years, their distribution appears again as more northerly, but new tagging studies are needed to confirm this. It is probable that changes in occurrence of this species in Norwegian waters reflect combined effects of changes in both migration patterns and population size.
Spurdogs form large schools which can result in large quantities being caught, once encountered. Males and females often form their own schools, as do large and small fish. Females give birth to a small number (7–11) of live offspring after a two-year gestation period. Therefore, capturing large schools of pregnant females has a significant effect on future recruitment levels. For this reason, the spurdog, like many other shark species, is considered particularly vulnerable to overexploitation. Nevertheless, spurdog in other areas appear to be able to rebuild after substantial overfishing.
Status, advice and fishery
The northeast Atlantic spurdog stock has undoubtedly been very large and has provided a basis for valuable fishing for over a hundred years. During the 40-year period 1950–1990, annual landings of 30,000–60,000 tonnes were reported. Knowledge about the stock is incomplete, but according to the analyzes of ICES, the population was gradually reduced throughout this time period and in 1990 was only 20% of the size just after the Second World War. In the last 20 years, fishing has declined significantly, and from 2005 on the stock has not been overfished. During this time, the population has apparently had a steady but relatively slow growth.
Spurdogs grow slowly, become sexually mature late and only give birth to 7–20 cubs every other year. It can therefore take many years before the spawning stock can recover, even without any fishing. ICES therefore recommended that no direct fishing shall be carried out on spurdog in 2019 and 2020, and that by-catch was only allowed as part of a comprehensive management plan.
However, the stock situation is still somewhat uncertain, especially because of sparse data from Norwegian waters. Efforts are therefore being made to obtain a better data foundation for future stock analyzes.
Fishery and management
Spurdog has long been sought after both for the liver oil and for the meat, but it is also often regarded as a problem species, which, due to its abundance, its spines and its sandpaper skin, creates problems for fishing for other species. Traditionally, the UK, Ireland, France and Norway have fished the most northeast Atlantic spurdog. Fishing has taken place in the North Sea, west of Scotland, in the Irish Sea and in Norwegian waters, mainly through direct fishery using longline and gillnet, but also as by-catch in trawl fishing.
In recent years, increasingly stricter regulations have been introduced, and several measures have made it less attractive to fish spurdog. Both in Norwegian waters and in the EU, there has been a ban on direct fishing, as well as strict by-catch regulations. One side effect of this is that fishing mortality now does not get included into the landing statistics.
The importance of fishery for population development is strongly dependent on which parts of the population are fished. With increased knowledge of both the catch composition and how the stock utilizes our waters, more targeted management measures can be implemented such as area and seasonal restrictions, which affect other fisheries to a lesser extent.
Published: 18.12.2018 Updated: 06.04.2020