Probabilistic maturation reaction norm trends reveal decreased size and age at maturation in an intensively harvested stock of pikeperch Sander lucioperca

Kokkonen, Eevi; Vainikka, Anssi; Heikinheimo, Outi

doi:10.1016/j.fishres.2015.01.009

Cited by 24 publications

(25 citation statements)

References 50 publications

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“…The top‐down effects may have been difficult to identify also, because many of the study lakes were intensively fished as indicated by the scarcity of large (>50 cm) pikeperch in the gillnet samples. Productive lakes could attract high fishing pressure that truncates the predator population's size structure (Kokkonen, Vainikka, & Heikinheimo, ) and weakens its total predatory effect. However, there was only a marginal difference in pikeperch BPUE, when lakes managed with the former national 37 cm minimum size limit (128.5 g) were compared to lakes with a locally increased minimum size limit (189.9 g; Appendix S2).…”

Section: Discussionmentioning

confidence: 99%

Structural equation models suggest that bottom‐up processes override top‐down processes in boreal pikeperch (Sander lucioperca) lakes

et al. 2019

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Inter‐relations between water quality and piscivore populations have remained poorly studied but their quantification is crucial for the ecosystem‐based management of inland waters. Here, we aimed to estimate the relative strength of bottom‐up and top‐down trophic interactions between water quality and fish community composition using a comparative approach. Our main hypothesis was that lakes with an abundant piscivore (mainly pikeperch, Sander lucioperca, Percidae) stock would have better water quality than similar lakes with a poor piscivore stock. We used structural equation models on biomass catch per unit of effort data from standard gillnet test fishing to examine the effects of predators (pikeperch, pike [Esox lucius, Esocidae] and piscivorous perch [Perca fluviatilis, Percidae]) on cyprinids (Cyprinidae), and the effects of cyprinids, nutrients, and lake depth on water quality measured as chlorophyll‐a concentration and turbidity. We derived the dataset covering a single summer snapshot of 138 Finnish pikeperch lakes from national databases. Nutrients and lake depth index, the main principal component describing positive effects of nutrient concentrations and negative effects of lake depth, had a positive effect on chlorophyll‐a concentration and turbidity. Pikeperch had a detectable negative effect on both planktivorous and benthivorous cyprinids. While pike also had a negative effect on benthivorous cyprinids, both groups of cyprinids had a positive effect on pikeperch and pike. Supporting the strong, fish‐independent bottom‐up regulation, no significant relationships were detected between the cyprinids and water quality. This study suggests that the bottom‐up effects override the top‐down effects, and despite pikeperch is an efficient piscivore, the observed stock levels did not cascade down to improved water quality. Thus, in lake restoration, reductions of nutrient loading appear more efficient than biomanipulation aimed to strengthen the top‐down links.

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Section: Discussionmentioning

confidence: 99%

Structural equation models suggest that bottom‐up processes override top‐down processes in boreal pikeperch (Sander lucioperca) lakes

et al. 2019

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“…However, this also means that long-migrating fish face a higher mortality risk in the Gulf of Bothnia because of the heavy commercial fishing pressure present along the coast. The effect of fishing selection on the size of whitefish has been well documented by Heikinheimo and Mikkola (2004), and the consequences are also reflected in the early maturation of fish (Kokkonen, Vainikka & Heikinheimo, 2015).…”

Section: Discussionmentioning

confidence: 82%

“…However, this also means that long‐migrating fish face a higher mortality risk in the Gulf of Bothnia because of the heavy commercial fishing pressure present along the coast. The effect of fishing selection on the size of whitefish has been well documented by Heikinheimo and Mikkola (), and the consequences are also reflected in the early maturation of fish (Kokkonen, Vainikka & Heikinheimo, ). According to Leskelä, Jokikokko and Huhmarniemi (), about 60% of tagged whitefish stocked in the mouth of the River Kemijoki were caught in the Bothnian Sea and in the Quark during their feeding migration.…”

Section: Discussionmentioning

confidence: 87%

Short feeding migration associated with a lower mean size of whitefish in the River Tornionjoki, northern Baltic Sea

Jokikokko

Hägerstrand

Lill

2018

Fisheries Management Eco

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The size of anadromous whitefish caught with dip nets in the River Tornionjoki in the northern part of the Gulf of Bothnia has decreased during recent decades. To find an explanation for this trend, ascending whitefish were sampled in the lower part of the river in August 2016, and they were divided into two groups according to fish length. The length of the SMALL group was ≤ 32 cm (n = 32) and that of the LARGE group ≥ 33 cm (n = 65). The elemental analysis of otoliths revealed that the barium concentration was clearly higher in otoliths from the SMALL group compared to the LARGE group. This indicates that the fish in the LARGE group had migrated to feed further south in the Gulf of Bothnia, with a higher salinity, than the fish in the SMALL group. Because of this migration difference, and a decline in the gillnet effort, especially in the feeding areas near the river mouth, it is assumed that proportionally more fish in the SMALL group are able to ascend the river to spawn than previously, thus decreasing the mean size. At the same time, the heavy gillnet fishery in the south removes fish from the LARGE group.

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“…A similar trend of a decreasing mean size of specimens in the spawning stock of anadromous whitefish has been observed in the Tornionjoki River (Jokikokko & Huhmarniemi, ). The changes in the age structure of the spawning population may also lead to changes in the age at maturation, as has occurred among gill‐netted pikeperch ( Sander lucioperca ) in the Baltic Sea (Kokkonen et al, ). Usually, selective fishing simultaneously changes both the growth rate and age at maturation (Grift, Rijnsdorp, Barot, Heino, & Dieckmann, ; Hutchings, ).…”

Section: Discussionmentioning

confidence: 99%

Different growth trends of whitefish ( Coregonus lavaretus ) forms in the northern Baltic Sea

et al. 2019

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The sea growth of two whitefish forms, anadromous (Coregonus lavaretus lavaretus) and sea‐spawning (Coregonus lavaretus widegreni), was analysed using samples collected from the commercial sea catch in the Gulf of Bothnia (GoB) in the northern Baltic Sea during 1998–2014. In the GoB area, these two forms are possible to identify because the gill‐raker number and size at maturity vary between forms. The growth rate of the forms is linked to their feeding area. Sea‐spawning whitefish, which has a feeding migration near its home site, was shorter in the northern GoB (66°N–64°N) at the ages of 3–11 than those in the southern GoB (64°N–60°30′N). In the data, most whitefish were caught with gill nets in the GoB. The mesh sizes of gill nets capturing the anadromous form were mostly 35–45 mm, while those capturing the sea‐spawning form were <35 mm in the northern GoB. It is likely that the different growth trends for small and large whitefish were connected with differences in their recruitment for fishing. The length of anadromous females at the age of four sea years increased significantly, but the length of six‐year‐old anadromous female whitefish decreased over the catch years from 1998–2014. In contrast, the length of slow‐growing sea‐spawning whitefish of six years or older increased significantly in relation to the catch year in the gill‐net catch. The increase in the growth of young age groups in both forms was probably associated with the increasing temperature and the low fishing pressure on small fish. The decreasing age at capture for both forms and the depression of the mean size of old anadromous whitefish are signs of high fishing pressure with a high gill‐net effort that selectively removes the largest and oldest individuals of both forms.

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Probabilistic maturation reaction norm trends reveal decreased size and age at maturation in an intensively harvested stock of pikeperch Sander lucioperca

Cited by 24 publications

References 50 publications

Structural equation models suggest that bottom‐up processes override top‐down processes in boreal pikeperch (Sander lucioperca) lakes

Structural equation models suggest that bottom‐up processes override top‐down processes in boreal pikeperch (Sander lucioperca) lakes

Short feeding migration associated with a lower mean size of whitefish in the River Tornionjoki, northern Baltic Sea

Different growth trends of whitefish ( Coregonus lavaretus ) forms in the northern Baltic Sea

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