Abstract

Analysis of commercial catches reveals a serial depletion of some oceanic fish stocks over time, resulting in fisheries focusing on increasingly smaller species closer to the base of the food chain. This effect, described as fishing down the marine food web, is observed when the trophic level of the catch declines over time, raising concerns about the ecosystem impacts of fishing. Freshwater systems also experience harvest, yet do not appear to commonly show the same fishing down response perhaps because time series are too short to witness early depletions, fishing is often recreational, or other factors like stocking and invasive species influence patterns. Here we make use of extensive catch records from Lake Simcoe dating back to the 1860s, to examine if fishing down effects are observed in this highly exploited Canadian inland lake. We measured 2 commonly used indicators from catch data, mean trophic level (MTL) and fishing-in-balance (FiB), and compared trends between a historical period dominated by commercial fishing and a contemporary period when commercial fishing ceased and recreational fishing effort increased. We found a striking difference between the 2 time periods, with MTL (and to some extent FiB) declining during commercial fishing but increasing during recreational fishing. However, indicators either increased or decreased due to invasive species and increased due to stocking. We show that while declining MTL can occur in a freshwater lake, the trajectory can be altered by a switch to recreational fishing, as well as stocking and invasive species.

Keywords

Great Lakes; angling; lake trout; Bythotrephes; dreissenid mussels

Published in

Proceedings of the National Academy of Sciences of the United States of America
2019, Volume: 116, number: 40, pages: 19995-20001
Publisher: Proceedings of the National Academy of Sciences

UKÄ Subject classification

Ecology


Publication identifier

DOI: https://doi.org/10.1073/pnas.1908272116

Permanent link to this page (URI)

https://res.slu.se/id/publ/112723