Long‐Term Evaluations of Length Limit Regulations for Northern Pike in Minnesota

Abstract

The effects of maximum, minimum, and slot length limits on the sizes and relative abundance of northern pike Esox lucius were evaluated in 22 Minnesota lakes. The regulations were implemented in 1989–1998 and lasted 9–15 years. As preregulation information was available back to the 1970s, the evaluation periods covered 21–37 years. Comparisons were made with reference populations from 47 ecologically similar lakes during the same extended period. Although the regulations did not achieve management objectives in every lake, the broader‐scale, statewide finding was that they improved the size structure of northern pike populations but produced no consistent trends in relative abundance. The improvements were detected against the backdrop of reference populations that initially appeared to have similar sizes and relative abundances. Maximum length limits protecting fish over 20, 22, and 24 in produced significant long‐term increases in the percentages of northern pike 24 in and longer and 30 in and longer compared with the reference populations. Lakes with 30‐in minimum length limits had increased percentages of northern pike 20 in and longer, but the improvements did not carry over to fish 30 in and longer. A mix of slot length limits produced results that are more difficult to interpret but generally improved size structure. A metaanalysis incorporating all of the length regulations indicated that the changes in northern pike size structure in regulated lakes were very large for an ecological experiment. Length limits protected large northern pike, with the expectation that lower yields were an acceptable trade‐off for producing larger fish for recreational fisheries. This study reveals the range and magnitude of responses we can reasonably expect from length limits as well as the substantial value of conserving large fish when the goal is improved population size structure.

Overfishing disrupts an ancient mutualism between frugivorous fishes and plants in Neotropical wetlands

“…Although minimum legal capture sizes have been established to preserve reproductive potential, this management strategy does not consider the role of these fishes in wetland plant regeneration. A scientifically robust management plan that preserves larger individuals, such as maximum size thresholds (e.g., Pierce, 2010), can help safeguard a key ecosystem process.…”

Consequences of size-selective harvesting and changing climate on the pikeperch Sander lucioperca in two large shallow north temperate lakes

“…Additionally, the maximum size limit is difficult to apply to commercial fisheries because the gear utilised in large Estonian lakes does not allow for the application of the catch and release fishing practices that are utilised in recreational angling (Berkeley et al, 2004;Pierce, 2010). However, measures need to be introduced to avoid situations in which size-selectivity leads to reduced diversity at the individual, population, and ecosystem levels.…”

“…These lakes have been centres of human activities for centuries, and these analyses add new knowledge to help us to understand the effects of heavy fishing in freshwater ecosystems in the north temperate region with variable weather conditions. Thus far, only a few long-term studies are available in the literature (Pierce, 2010). The aim of this study was to elucidate the effects of sizeselective fishing on the pikeperch populations of the Lakes Peipsi and Võrtsjärv in changing environmental conditions and fishery management practices.…”

Hook Selectivity in an Artisanal Spotted Rose Snapper Lutjanus guttatus Fishery on the Nicoya Peninsula, Costa Rica

“…Preservation of larger fish may also be important, since older fish often contain more and higher quality eggs (Love et al 1990;Berkeley et al 2004) and have longer spawning periods (Berkeley et al 2004). While MSLs have proven effective at preserving fish smaller than the limit in some fisheries (Pierce 2010), they may have little impact on larger fish (Arlinghaus et al 2010). Some researchers believe that slot limits (joint upper and lower limits on the size of fish that may be caught) should be enforced to preserve the older, possibly more fecund members of the population (Arlinghaus et al 2010).…”