Assessing the relative importance of temperature, discharge, and day length on the reproduction of an anadromous fish (Alosa alosa)

Abstract

Climate change threatens anadromous fishes such as the allis shad (Alosa alosa)populations of which have declined since the 20th century in Europe. Sensitivity to climate change could be quantified by determining the fish's spawning behaviour, defined as the timing of reproduction (i.e. spawning events) as a function of temporally variable environmental factors. The cues that fish use to time reproduction could determine their response to climate change.2. A machine learning technique (boosted regression tree) was calibrated using a 14-year dataset composed of daily measures of environmental factors and fish occurrences during reproduction. The boosted regression tree provides complete insight into the complex relationship between the spawning probability, i.e. the probability for a fish to reproduce, and environmental factors that might evolve with climate change.3. The spawning probability was positively related to day length (44.6%) and water temperature (34.7%) and negatively related to river discharge (20.7%). Optimal reproductive conditions corresponded to a difference in day length between 0 and 0.04 hr, a water temperature between 15 and 26°C and a river discharge between 55 and 665 m 3 /s; these conditions are currently being utilised by allis shad populations in the Garonne and Dordogne rivers, France.4. This study highlights the relative influence of environmental factors on the observed spawning period as well as the evolution of habitat suitability during the 14-year period. The novelty of this study stems from assessing population process data, i.e. the occurrence of fish reproduction, rather than mere occurrence data in an ecological niche model study. Climate change may lead to a shift in spawning phenology, as the water temperature and river discharge will also change. Therefore, conservation plans need to integrate these effects on spawning grounds. K E Y W O R D Sboosted regression tree, climate change, ecological niche, ecospat, migratory fish How to cite this article: Paumier A, Drouineau H, Boutry S, Sillero N, Lambert P. Assessing the relative importance of temperature, discharge, and day length on the reproduction of an anadromous fish (Alosa alosa). Freshwater Biology.

Disordered Climate Threatens Short-Distance Migrants

“…With climate change leading to an increasingly disordered climate [19][20][21] , short-distance migratory species need more attention and conservation actions. As a disordered climate could severely impact sensitive phenology and stabilized phenology responds to climate change with a time lag, the mismatch between sensitive phenology and stabilized phenology within the same short-distance migrants would impact their breeding success, although phenotypic plasticity could provide the potential for organisms to respond rapidly and effectively to environmental change 7,31 . In our survey conducted on 5 June 2020, 19.35% of G. przewalskii individuals captured in Qinghai Lake near the Buha River estuary were identi ed as postspawning when the G. przewalskii breeding group had not migrated into the traditional spawning habitats.…”

“…Climate change alters every biome and affects nearly every species [1][2][3][4] , especially migratory species [5][6][7][8][9] . Species with shorter migration distances are better able to predict the onset of spring at their breeding sites than species with longer migration distances do 10 .…”

“…We monitored two phenology indicators, spring migration (arrival dates) and gonadal development ( +), and two population dynamics indicators, migrating population size and larval ux. Following the framework of environmental drivers of variation and exibility in sh migration 7,25 , we monitored two environmental indicators: air temperature (indirectly indicating river water temperature) and river discharge. Furthermore, we analyzed the variation in spring migration, gonadal development, migrating population size, larval ux, air temperature and river discharge to verify our hypothesis.…”

Disordered climate threatens short-distance migrants

“…It is clear that in response to climate change, different species shift their phenology at different rates, which causes mismatches between the phenology of interacting phenology and stabilized phenology responds to climate change with a time lag, the mismatch between sensitive phenology and stabilized phenology within the same short-distance migrants would impact their breeding success, although phenotypic plasticity could provide the potential for organisms to respond rapidly and effectively to environmental change (Paumier et al 2020;Senner et al 2020). In our survey conducted on 5 June 2020, 19.35% of G. przewalskii individuals captured in Qinghai Lake near the Buha River estuary were identified as postspawning when the G. przewalskii breeding group had not migrated into the traditional spawning habitats.…”

“…Climate change alters every biome and affects nearly every species (Freeman et Cohen & Satterfield 2020; Paumier et al 2020). Species with shorter migration distances are better able to predict the onset of spring at their breeding sites than species with longer migration distances do (Visser et al 2009).…”