State-space modeling of multidecadal mark–recapture data reveals low adult dispersal in a nursery-dependent fish metapopulation

Abstract

Quantifying connectivity within fish metapopulations is an important component in understanding population dynamics and providing an evidence base for assessment and management. We investigate metapopulation connectivity of the common sole (Solea solea) in the Eastern English Channel (EEC). The EEC common sole stock is currently assessed as a single and spatially homogeneous population, but connectivity induced through adult movements within this stock and with nearby stocks remains unknown. To fill this knowledge gap, we developed a state-space mark–recovery model, designed to estimate adult connectivity using mark–recapture data from multiple release experiments from 1970 to 2018 across the EEC and adjacent management areas. The model estimates seasonal fish movements between five predefined areas, Western English Channel, Eastern English Channel (split into three discrete sub-areas), and North Sea. Over 32 000 fish were tagged, 4036 of which were recovered via fisheries. Our results suggest minimal large-scale adult movements between these areas; movements among spatial units within the EEC were very low with even lower levels of immigration from areas adjoining the EEC. Our results support the hypothesis of segregated populations within the EEC. The importance of accommodating population substructure in the fisheries management is considered.

Complementarity and discriminatory power of genotype and otolith shape in describing the fine-scale population structure of an exploited fish, the common sole of the Eastern English Channel

“…First, the connection between subunits could have been stronger in 2018. This explanation is unlikely since a mark-recapture study has suggested low adult movement across the EEC over decades [ 22 ], which is in line with the spatial genetic pattern found in 2017. Second, the observed differences could be due to a library effect.…”

“…Based on the EEC underwater topography and the results of the biophysical modelling [ 53 ], a functioning in three subunits have been hypothesized ( Fig 1 ). Life history traits at the population scale supported the spatial structure in three putative subunits ([ 59 , 60 ]; Fig 1 ) and mark-recapture experiments estimated low exchanges between these subunits ([ 22 ]; Fig 1 ). However, the population structure has not been investigated yet at the individual level, nor a potential genetic differentiation.…”

“…In addition, density-at-age analysis suggested the isolation of the SW subunit from the rest of the stock [ 59 , 60 ]. Moreover, the results of a mark-recapture study demonstrated low dispersal across the EEC stock [ 22 ]. Therefore, it seems that the low connectivity observed at early life stages [ 53 , 58 ] is maintained at the adult stage and contributes to the weak metapopulation structure.…”

“…For the genetic analysis, a total of N g = 215 ( Table 1 ) adult common sole was sampled on the spawning grounds in French, off the rivers Seine (SW) and Somme (NE), and UK waters ( Fig 1 ) in April and May 2017 and 2018 from commercial fishing vessels during tagging experiments [ 22 ]. An exception was made in July 2018, when individuals from the English part of the EEC were collected during the UK Beam Trawl Survey.…”

“…A wide range of methods exist to assess the structure and connectivity of marine fish populations [ 17 , 18 ]. Insights in population segregation are available from, among others, larval dispersal modelling [ 19 , 20 ], mark-recapture experiments [ 21 , 22 ] and natural tracers such as morphometry and meristics [ 23 – 26 ], microchemistry (e.g. [ 27 , 28 ]) and genetics [ 29 , 30 ].…”