Assessing connectivity patterns among management units of the Newfoundland and Labrador shrimp population

Abstract

The Eastern Canadian northern shrimp population, representing one of the most important fisheries in the region, decreased dramatically since the mid‐2000s to a historical low in 2017, but changes were not spatially uniform. Applying a biophysical model within Newfoundland and Labrador (NL) management areas, we investigated connectivity processes during the long pelagic larval phase (2–3 months) of Pandalus borealis and key drivers of larval dispersal in different environmental conditions. We selected 3 years representative of contrasting North Atlantic Oscillation (NAO) phases to assess potential larval dispersal patterns of the northern shrimp population in NL, and hierarchically assessed the impact of the timing of release (yearly and daily), release location, and vertical migration behaviour on shrimp larval dispersal. Overall, we found that populations located on the northern Newfoundland and Labrador shelf supplied potential settlers to southern populations because of the dominant Labrador Current. Ocean circulation and current velocities during the NAO positive year differed from other years, generating contrasting settlement spatial patterns. Larval release location and vertical migration behaviour were the two most important influences on the strength of larval supply and settlement patterns. Inclusion of diel and ontogenic swimming behaviour increased settlement success of larvae released from inshore areas, regardless of study years. Our study improves understanding of northern shrimp stock‐recruitment relationships, their sensitivity to changing environmental conditions, and spatially non‐homogeneous population decline for bentho‐pelagic species with a long larval phase, which could potentially help improve management strategies.

3-D ocean particle tracking modeling reveals extensive vertical movement and downstream interdependence of closed areas in the northwest Atlantic

“…time step was chosen for releasing and following particle trajectories to ensure that particles do not cross the grid in a single time step. Horizontal diffusion in the study region previously has been reported as 50 38 , 64 39 and 150 m 2 s −140 and the spatial distribution of modeled particles did not differ markedly with applications of 100 and 200 m 2 s −120 . Particle spacing of 0.01° was generally employed 20 except for the calculation of back-tracked transit time distributions for the assessment of functional connectivity, where a finer spacing of 0.005° was used to allow more particles to be both released, and thus to enter the closed areas with smaller spatial size (e.g., Areas 7-9).…”

Potential impact of climate change on northern shrimp habitats and connectivity on the Newfoundland and Labrador continental shelves

“…Shrimp larvae were released and moved forward and vertically every 6 hr following a fourth‐order Runge–Kutta scheme based on horizontal oceanographic circulation data from the NLRM, and tracking information was recorded daily. Vertical current velocities were not considered in larval dispersal because they were negligible relative to horizontal velocities and larval vertical migration behaviour (Le Corre et al., 2019). We used the CMS basic particle simulator associated with the stochastic diffusivity component (random‐walk, with the diffusivity coefficient K h = 64 m 2 /s based on Okubo, 1971), a vertical migration module (see below), as well as a module that prevents larvae from settling at the coast (i.e., particles stay in the water and keep moving) by using a simpler interpolation method (i.e., tri‐linear instead of tri‐cubic interpolation) in the vicinity of land (Paris et al., 2013).…”

“…However, the most important northern shrimp fisheries, located mainly on the Newfoundland and Labrador (NL) shelves, have declined considerably since the mid‐2000s, but the cause of the decline remains uncertain (DFO, 2019). Northern shrimp behave as a metapopulation and display stream‐like connectivity patterns (e.g., from North to South on the NL shelf) at the scale of the northwest Atlantic Ocean (Jorde et al., 2015; Le Corre et al., 2019, 2020). Despite this basic knowledge, we still know very little on how environmental conditions and climate change will impact the preferred habitat and connectivity of bentho‐pelagic species with a long dispersal phase.…”

Migration, Dispersal, and Gene Flow of Harvested Aquatic Species in the Canadian Arctic

“…Following metamorphosis, ovigerous females return to shallow waters where larvae are released. The pelagic life stage can last up to 3 months [77] and is highly influenced by oceanographic currents while settlement patterns are heavily influenced by the release location as well as the vertical migration behavior [78]. However, discrepancies still exist in our understanding of life-stage specific habitat preferences between northern and striped shrimp but there is a general agreement that Pandalus montagui are found in shallower (200-500 m) and cooler (−1 to 2°C) waters throughout their development [79].…”