Future-proofing a Swedish shark conservation success story
The north-western Atlantic spiny dogfish has returned to Swedish waters after reaching near collapse. When fishing quotas reopened in 2023, some gaps in ecological knowledge became obvious. Petter is intent on closing these and improving understanding of spiny dogfish movements and temporal aggregations and where the dogfish are most vulnerable to commercial and recreational fishing. He is using ongoing recreational fishing to sample spiny dogfish along the Swedish west coast to find out where and how they move. He’s also hoping to identify potential pupping grounds and nurseries, assess bio-accumulation of contaminants and assist authorities in conserving a coastal predator.
Petter Lundberg
Born and raised in the Swedish north, I had wilderness at my doorstep. From an early age, I followed my older siblings on their adventures. My fascination for the world around us grew with every step, especially for the animals. This escalated the first time I put my head underwater. The Bay of Bothnia might not be known for species richness, nor warm, clear water, but that did not bother me. Breath by breath I tried my best; I sank until I learned to swim, and since then I have been exploring the ‘silent world’ beneath the waves.
Population dynamics of spiny dogfish – the ‘last’ coastal predator in Swedish waters
We aim to understand the spatial distribution and population dynamics of spiny dogfish along Sweden’s west coast and thereby identify important areas, such as mating and pupping grounds, and where the species is most exposed.
Spiny dogfish stock has returned to Swedish waters thanks to efficient management, recovering from virtually collapsed to the point that a fishing quota reopened in 2023. However, the stock estimate is riddled with uncertainty, and spatial ecology data are scarce. Swedish authorities recently addressed this shortcoming and expressed the need to improve knowledge about spiny dogfish movements and temporal aggregations, and where the species is most vulnerable to commercial and recreational fishing.
Marine ecosystems around the world are under great stress from threats such as climate change, intense fishing pressure and the emission of environmental toxins. Large predators with a slow growth rate and a low reproductive rate are among the species most affected. Swedish waters are no different and the number of top predators hunting in the coastal waters of Kattegat and Skagerrak has declined drastically, resulting in an unbalanced ecosystem.
After having virtually collapsed, the north-western Atlantic spiny dogfish stock has now returned to our coastal waters, thanks to a precautionary approach that banned targeted fishing. According to the International Council for the Exploration of the Sea (ICES), the stock had recovered to such an extent that it was decided to reopen a fishing quota in 2023. This estimation is based on trawl surveys, a monitoring method associated with uncertainty for the spiny dogfish, as its sex-biased schooling behaviour results in irregular catches. Swedish authorities recently recognised this knowledge gap and expressed the need to find out more about spiny dogfish movements, temporal aggregations and where the species is most vulnerable to commercial and recreational fishing.
Last year, we at the Department of Wildlife, Fish and Environmental Studies, at the Swedish University of Agricultural Sciences, initiated an acoustic telemetry study of spiny dogfish. Although powerful, the technique is spatially limited as it relies on a tagged shark being close enough to a receiver for its signal to be detected. We will now complement our telemetry study with large-scale sampling along the entire west coast using ongoing recreational fishing. Using both methods, the planned study represents a major step towards a better understanding of how we can best manage the spiny dogfish stock and thereby maintain at least one viable coastal predator on the Swedish west coast.
- To make use of ongoing recreational fishing to measure and sample spiny dogfish along the Swedish west coast, thereby assessing the species’ spatial distribution and population dynamics.
- To identify potential pupping grounds and nursery areas through ultrasound analysis of sexually mature females and size structure analysis.
- To assess the bio-accumulation of pharmaceuticals and other persistent contaminants.
- To communicate our results to authorities and thereby assist in the conservation of a viable coastal predator in Kattegat and Skagerrak.