Hiding in numbers or the benefit of travelling with others

The Norwegian Barents Sea system is highly productive with several commercially important fish stocks that are the Northeast Arctic cod Gadus morhua, the Northeast Arctic haddock Melanogrammus aeglefinus, capelin Mallotus villosus, and juvenile stages of Norwegian spring-spawning herring Clupea harengus.

Many studies have already shown how these species interact with each other (see previous posts her, her, her and her). All have the particularity to drift together during one of their most sensitive life stage (i.e., the larval stage). How they interact during the drift remains unknown. In earlier work, Ferreira et al (2020) show how the increase of the spatiotemporal overlap with its prey is affecting positively the recruitment of young cod (survival to be big enough to be fished, ca 3 years of age) that were spawned and hatched in the Lofoten (see post).

Here we use the same approach to asses if the fact of drifting together is a benefit or a disadvantage in term of survival at a later stage. For this, we calculate the spatiotemporal overlap between fishes and between fish and prey as described in Durant et al. (2005). We quantified the spatiotemporal overlap through time from 1959−1993 and compared that with recruitment.

Our analyse show that, for cod only, the overlaps between larvae and competing species and/or food have an effect on recruitment. This means that for cod it is a disadvantage to drift together with the other fish hatching on the Norwegian coast, haddock and capelin, while the later may take advantage. For instance, capelin get advantage to drift with prey and haddock seems not to be affected by it except for when capelin larvae are present.

The study of Ferreira et al 2024 sheds light on an important topic in fish ecology that is how the first weeks and months of life of fish larvae are affecting recruitment. Finding that the overlaps between larval cod and competing species and/or food have a negative influence on cod recruitment whereas the relationships pertaining to haddock and capelin is variable, may indicate a potential competition between these species. These results expand our understanding of how these species may use their habitat to cope with new environmental stressors.

Reference:

Ferreira ASA, Langangen Ø, Yaragina NA, Prokopchuk IP, Durant JM (2024) How the spatio-temporal overlap of cod, haddock, and capelin larvae affects their recruitment in the Norwegian–Barents Sea system. Marine Ecology Progress Series, 734: 79-90.

Ferreira ASA, Stige LC, Neuheimer AB, Bogstad B, Yaragina N, Prokopchuk I, Durant JM (2020) Match-mismatch dynamics in the Norwegian-Barents Sea system. Marine Ecology Progress Series LFC:LFCav5

Durant JM, Hjermann DO, Anker-Nilssen T, Beaugrand G, Mysterud A, Pettorelli N, Stenseth NC (2005) Timing and abundance as key mechanisms affecting trophic interactions in variable environments. Ecology Letters 8:952-958