Lessons learned from practical approaches to reconcile mismatches between biological population structure and stock units of marine fish

Recent advances in the application of stock identification methods have revealed inconsistencies between the spatial structure of biological populations and the definition of stock units used in assessment and management. From a fisheries management perspective, stocks are typically assumed to be discrete units with homogeneous vital rates that can be exploited independently of each other. However, the unit stock assumption is often violated leading to spatial mismatches that can bias stock assessment and impede sustainable fisheries management. The primary ecological concern is the potential for overexploitation of unique spawning components, which can lead to loss of productivity and reduced biodiversity along with destabilization of local and regional stock dynamics. Furthermore, ignoring complex population structure and stock connectivity can lead to misperception of the magnitude of fish productivity, which can translate to suboptimal utilization of the resource. We describe approaches that are currently being applied to improve the assessment and management process for marine fish in situations where complex spatial structure has led to an observed mismatch between the scale of biological populations and spatially-defined stock units. The approaches include: (i) status quo management, (ii) "weakest link" management, (iii) spatial and temporal closures, (iv) stock composition analysis, and (v) alteration of stock boundaries. We highlight case studies in the North Atlantic that illustrate each approach and synthesize the lessons learned from these real-world applications. Alignment of biological and management units requires continual monitoring through the application of stock identification methods in conjunction with responsive management to preserve biocomplexity and the natural stability and resilience of fish species.</p

Evidence for inshore spawning of Atlantic cod (Gadus morhua) in Trinity Bay, Newfoundland, from 1991 to 1993

The objective of this thesis was to determine if northern Atlantic cod (Gadus morhua) spawn in Trinity Bay, Newfoundland. Prior to this study, only indirect evidence existed for inshore spawning by cod along the northeast coast of Newfoundland. Research reported here confirms that Atlantic cod spawn in Trinity Bay, Newfoundland, during the early summer on an annual basis. This conclusion is supported by evidence from three lines of investigation. These are 1) the observed progressive maturation of inshore cod from spawning to spent condition, 2) direct observation of a spawning aggregation of cod in Trinity Bay, and 3) the presence of recently spawned cod eggs (≤ 10 days old) in the bay. A spawning "window" in Trinity Bay from mid-June to early July is estimated for the period of 1991-1993. This timing of spawning was delayed relative to offshore spawning components of Atlantic cod at similar latitudes. A simple model was proposed to explain this delay based upon the temperature to which inshore cod were exposed during the winter. Predictions of oocyte development times in female Atlantic cod were in phase with observed spawning times. Predictions using cumulative degree-days calculated from monthly seawater temperature profiles were less able to explain the temporal component of the spawning window in Trinity Bay

<Session 1: Fish Telemetry I>Using underwater coded acoustic telemetry for fine scale positioning of aquatic animals

19–22 May 2015 Kyoto, JapanMeasurements of aquatic animal movements, activity, and energetics in nature have always been technologically challenging. In many species around the world, detailed movement and activity information is urgently required for a variety of reasons. Issues related to fishing pressure, habitat degradation, pollutants, and responses to environmental change are just a few of the many applications that require knowledge of the temporal and spatial movement patterns of aquatic animals. Here we describe the development and implementation of a new multi-receiver positioning system (VPS-VEMCO Positioning System) that can be used in a variety of biological applications to study the behavior of aquatic animals in nature. VPS is more suited to a larger variety of applications compared to existing positioning systems that are constrained by cost and equipment deployment limitations (e.g. wire connecting hydrophones). To date, VPS has been successfully used in small (3 receivers covering 2500 m_2) and large area studies (tens of kilometers_2) in lakes, rivers and ocean environments. We discuss the design and specifications of VPS, the factors that influence positioning accuracy, and some examples of VPS study designs

A study of northern Atlantic cod (Gadus morhua) of eastern Newfoundland and Labrador as a metapopulation

I present a model of intrapopulation structure in northern Atlantic cod (Gadus morhua) inhabiting the coastal and continental shelf regions off northeast Newfoundland and Labrador based on metapopulation dynamics. I suggest that the metapopulation concept may best explain the historical patterns and present day observations of northern cod distribution. Evidence for subpopulation structure is assembled from new and published data sources, including studies of spawning time and location, migration behaviour, and genetic variation. A theoretical model of northern cod metapopulation dynamics is derived from the simple model of Levins (1970). I consider the various spawning components of northern cod historically centered on the offshore banks and in coastal bays as subpopulations of a northern cod metapopulation. I modify the Levins (1970) model by separating the probability of subpopulation extinction into two component probabilities representing: (1) natural processes and (2) the effects of fishing. Metapopulation theory predicts that fewer suitable areas (spawning grounds) will be occupied as population abundance declines. The corollary prediction is that as population abundance recovers, spawners will recolonize the currently unoccupied spawning areas. The agents of colonization may be migratory adult fish and straying larvae. The model supports the current view that overfishing may have played an important role in the extinction of northern subpopulations off Labrador

Impact of Soil Characteristics and Weed Management Practices on Glyphosate and AMPA Persistence in Field Crops Soils from the St. Lawrence Lowlands (Quebec, Canada)

The use of glyphosate-based herbicides (GBHs) in industrial agriculture has intensified in the past decades, causing a growing concern about the occurrence and spatial distribution of glyphosate and its principal metabolite, aminomethylphosphonic acid (AMPA), in the environment. In 2014, glyphosate and AMPA content was measured in 45 soils from the St. Lawrence Lowlands (Quebec, Canada) before seeding and at harvest in soybean field crops using various weed management practices with or without GBH applications. At the same time, a recent history of agricultural practices and soil conditions was compiled for the sampled sites. The results of the study show that 91% of the samples contained detectable amount of either glyphosate or AMPA, with maximum values of 0.47 mg·kg−1 and 1.16 mg·kg−1 for glyphosate and AMPA, respectively. Surprisingly, detectable amounts of AMPA were measured in fields not treated with GBHs in 2014, whereas traces of both glyphosate and AMPA were detected in organic field crops, highlighting the potential spreading and/or persistence of both compounds in the environment. Glyphosate content was significantly higher in clay soils rich in exchangeable cations, such as Mg2+, K+ and Ca2+, which can contribute to the retention of glyphosate in soil via complexation processes

Variant colourations of Atlantic cod (Gadus morhua) in Newfoundland and Labrador nearshore waters

Adult cod (Gadus morhua) inhabiting continental shelf waters of the Northwest Atlantic typically display a countershaded colouration: a dark back gradating to a light underbelly. Some cod in Newfoundland and Labrador inshore waters have predominantly brown or red pigmentation. Cod inhabiting Gilbert Bay in Labrador often have golden-brown colouration, likely the result of an invertebrate diet rich in carotenoids, and are known in the vernacular as the “golden cod of Labrador”. To determine the stability of these variant colourations, we captured cod from Gilbert Bay, held them in a net pen and fed them a diet of fish. Over the 12-week experimental period, the variant coloured cod lost much of their brown or red pigmentation, and became countershaded. Because of its impermanence when cod switch from invertebrate to fish prey, variant colouration of cod can provide only provisional information about stock origin