Lake and species specific patterns of non-diadromous recruitment in amphidromous fish: the importance of local recruitment and habitat requirements

Abstract

Understanding migratory life histories is critical for the effective management and conservation of migratory species. However, amphidromous migrations (fish hatch in streams, immediately migrate to the sea for a feeding period and return to fresh water as juveniles) remain understudied owing to the difficulties of tracking tiny larval fish. Despite this, it has widely been assumed that amphidromous fish have open, resilient populations, with marine-rearing larvae dispersing widely during their pelagic phase. In the present study we tested the hypothesis that when an alternative freshwater pelagic habitat is available, non-diadromous recruitment will be the dominant process in sustaining amphidromous fish populations, with implications for their connectivity and resilience. Otolith microchemical analyses of five species (three Galaxias (Galaxiidae), two Gobiomorphus (Eleotridae)) from paired systems on the South Island of New Zealand indicated that when a suitable freshwater pelagic habitat existed downstream, non-diadromous recruitment was the primary population-sustaining process, typically contributing >90% of recruits. In addition, not all species recruited from all lakes, indicating the importance of the largely unstudied role of species-specific amphidromous larval requirements. The results of the present study emphasise the need to better understand the dynamics of individual populations of amphidromous fish, and highlight the importance of understanding species-specific early life history requirements to fully understand their distributions and management needs.

Carryover effects of larval environment on individual variation in a facultatively diadromous fish

“…Consistent with previous studies in the Waipori–Taieri system (Closs et al, ; Hicks et al, ), we observed Ba signatures that remained high in otolith cores and low concentrations of Sr compared to diadromous common bully (Hicks, ), and we could not conclude that any fish were purely diadromous. We instead found continuous variation in Sr/Ca of both larval and adult otoliths, which we cautiously interpret as variation along a salinity gradient from estuarine to pure freshwater.…”

“…The underlying mechanism of carryover effects remains generally unknown, likely because it is tied to the complex series of events associated with development and metamorphosis. Several studies have revealed the role of genetic architecture which binds traits across life stages (Aguirre, Blows, & Marshall, 2014), while evidence for environment-specific covariations of genes across life stages (Gutteling et al, 2007) suggests that carryover effects are them- Consistent with previous studies in the Waipori-Taieri system (Closs et al, 2003;Hicks et al, 2017), we observed Ba signatures that remained high in otolith cores and low concentrations of Sr compared to diadromous common bully (Hicks, 2012), and we could not conclude that any fish were purely diadromous. We instead found continuous variation in Sr/Ca of both larval and adult otoliths, which we cautiously interpret as variation along a salinity gradient from estuarine to pure freshwater.…”

To sea or not to sea? Multiple lines of evidence reveal the contribution of non‐diadromous recruitment for supporting endemic fish populations within New Zealand's longest river

“…Raw data were baseline corrected and converted to element/Ca molar ratios using the Trace_Elements and Trace_Elements_IS data reduction schemes in iolite (Paton, Hellstrom, Paul, Woodhead, & Hergt, ). To characterize the rearing environment of each fish, the portion of the trace corresponding to the pelagic larval period of each otolith was isolated (Hicks et al, ), and the mean element/Ca molar ratios for this period were calculated. This period was determined based on the presence of a Mn spike indicating the core (Ruttenberg et al, ), and the rapid changes in several elements (particularly Sr and Ba) associated with recruitment‐related habitat switching (e.g.…”

“…In New Zealand, amphidromy is considered to be the dominant strategy for around one‐third (about 10 species, excluding marine wanderers) of the indigenous fish fauna (McDowall, ), with newly hatched larvae carried downstream into the ocean by river flows before returning to fresh water as juveniles. Although the widespread dispersal of larvae has often been assumed (McDowall, ), patchy geographic distributions suggest that the larvae of some species, including crustaceans, (Morgan, Fisher, Miller, McAfee, & Largier, ) may have a greater degree of control over their distribution than first thought (Baker & Hicks, ; Hicks et al, ; Sorensen & Hobson, ; Warburton, Jarvis, & Closs, ; Yungnickel, ). Some researchers have suggested that passive larval dispersal away from natal habitats (passive dispersal hypothesis; Huey et al, ) may be an inherently risky strategy, and that although some dispersal undoubtedly occurs, remaining close to adult habitats (dispersal limitation hypothesis) may be preferable for some species, particularly those with specific adult habitat requirements (Hicks et al, ; Warburton et al, ).…”

“…In New Zealand, although amphidromy appears to be an obligate life‐history strategy for some migratory species, others exhibit the potential to recruit within fresh waters if suitable conditions exist (Closs, Smith, Barry, & Markwitz, ; David, Chadderton, Closs, Barry, & Markwitz, ; Hicks et al, ). For these ‘facultatively diadromous’ species, successful reproduction and recruitment within fresh water appears to be reliant, at least in part, on the availability of very slow‐flowing lotic or lentic water bodies capable of supporting the small planktivorous prey required by small fish larvae with limited gape size (Closs, Hicks, & Jellyman, ).…”