New paper: do spiny dogfish interact with each other?
- Lotte Dahlmo
- 4 days ago
- 2 min read
Spiny dogfish are fairly small sharks often assumed to inhabit bottom waters, but although they are rarely seen from shore, they play a big role in coastal ecosystems. They tend to form aggregations in which individuals of same sex and/or size tend to appear together, which makes them vulnerable to human activities like trawling and bycatch. As with other shark species, spiny dogfish rely on close physical contact for mating.
To understand these interaction patterns better, we tracked spiny dogfish in a fjord system in western Norway to see when, where, and how they aggregate. This information can help us identify important periods such as mating, which is crucial for protecting a species currently listed as Vulnerable.
Between October 2022 and April 2024, we tagged 74 sharks with acoustic transmitters that recorded their depth. By combining this with network analysis, we could look at how often sharks overlapped in time, space, and depth, and thus investigate their interaction patterns.
What did we find?
They interact a lot with spiny dogfish showing high “centrality,” meaning individuals interact with many others—especially males with other males.Depth had a small effect on interactions across the three interaction types (female-female, male-male, female-male), but a slightly larger effect on mixed-sex (female-male) interactions than same-sex interactions (female-female, male-male).
Mixed‑sex interactions peaked in August and September, in more confined areas than in other months. This suggests that these late‑summer aggregations may represent mating periods and important mating habitats.
Why it matters
If we know when and where spiny dogfish are likely to mate, we can better protect these sharks during critical life stages. For a slow‑reproducing species already facing global population declines, safeguarding key habitats could help prevent future dramatic losses.
This study was supported by the Norwegian Research Council through the LOST project (No. 325840), DTOTrack project (No. 353802), and NorTrack project (No. 350669).
