Higher abundance of adult pike in Baltic Sea coastal areas adjacent to restored wetlands compared to reference bays

Abstract

The abundance of pike, a keystone top-predator, have declined dramatically in the Baltic Sea since the 1990s likely owing to recruitment failure. It has been proposed that wetland restoration can aid the recovery of the pike stock by increasing the number of recruits produced by anadromous populations. Yet, no previous studies have addressed whether wetland restorations are associated with higher abundances of adult pike in the coastal habitat. To address this, we performed standardised rod-and-reel survey fishing in paired bays with and without wetlands across three coastal areas and 3 years. To estimate dispersal and the contribution of wetland pike to the coastal stock, we tagged captured pike with passive integrated responders (PIT) and employed PIT reader stations in wetland inlets. The results showed that pike abundances were on average 90% higher in bays with an adjacent wetland although the effect varied among areas. Moreover, PIT-data uncovered that wetland pike constituted a high proportion of the pike found in adjacent coastal habitats and that some wetland fish dispersed up to 10 km. These results support that wetland restoration is a valuable tool to aid the coastal pike stock and ultimately restore the function and services of the coastal ecosystem.

Predation and spatial connectivity interact to shape ecosystem resilience to an ongoing regime shift

“…The role of different drivers will vary along this heterogeneous coastline, meaning that measures need to be adapted to local conditions. Other studies also point to the importance of restoring and increasing access to freshwater spawning habitat 22 , 23 , 56 , limiting physical disturbance of sensitive areas 48 and reducing eutrophication 57 . It would also be valuable to consider the role of these measures in modifying resilience, especially since considerable unexplained variation remains.…”

Combining movement ecology and genetics to understand the ecology and evolution of a freshwater top predator (northern pike, Esox lucius) that has colonized brackish lagoons in the southern Baltic Sea: implications for management and conservation of weakly connected metapopulations

“…Another key action is control of excessive captures via passive gear (e.g., gill nets) prior to spawning as they might preferentially target mobile pike during their spawning migration. Such measures, and especially the restauration of wetlands, were shown effective in enhancing the abundance and size structure of adult pike in Baltic coastal habitats (Larsson et al 2015;Tibblin et al 2023) and will also help to maintain a genetic ecotype that is presently rare in Bodden lagoons. For supporting the brackish-adapted subpopulations, it is equally important to maintain connectivity to allow dispersal from foraging sites to spawning bays (Flink et al 2023).…”