Britten GL, Dowd M, Kanary L, Worm B. Extended fisheries recovery timelines in a changing environment. Nature Communications. 2017.
Abstract: Rebuilding depleted fish stocks is an international policy goal and a 2020 Aichi target under the Convention on Biological Diversity. However, stock productivity may shift with future climate change, with unknown consequences for sustainable harvesting, biomass targets and recovery timelines. Here we develop a stochastic modelling framework to characterize variability in the intrinsic productivity parameter (r) and carrying capacity (K) for 276 global fish stocks worldwide. We use models of dynamic stock productivity fitted via Bayesian inference to forecast rebuilding timelines for depleted stocks. In scenarios without fishing, recovery probabilities are reduced by 19%, on average, relative to models assuming static productivity. Fishing at 90% of the maximum sustainable rate depresses recovery probabilities by 42%, on average, relative to static models. This work reveals how a changing environmental context can delay the rebuilding of depleted fish stocks, and provides a framework to account for the potential impacts of environmental change on the productivity of wildlife populations more broadly.
Kanary L, Musgrave J, Tyson RC, Locke A, Lutscher F. Modelling the dynamics of invasion and control of competing green crab genotypes. Theoretical Ecology. 2014.
Abstract: Establishment of invasive species is a world-wide problem. In many jurisdictions, management strategies are being developed in an attempt to reduce the envi-ronmental and economic harm these species may cause in the receiving ecosystem. Scientific studies to improve understanding of the mechanisms behind invasive species population growth and spread are key components in the development of control methods. The work presented herein is motivated by the case of the European green crab (Carcinus maenas L.), a remarkably adaptable organ-ism that has invaded marine coastal waters around the globe. Two genotypes of European green crab have inde-pendently invaded the Atlantic coast of Canada. One genotype invaded the mid-Atlantic coast of the USA by 1817, subsequently spreading northward through New England and reaching Atlantic Canada by 1951. A sec-ond genotype, originating from the northern limit of the green crabs European range, invaded the Atlantic coast of Nova Scotia in the 1980s and is spreading southward from the Canadian Maritime provinces. We developed an integrodifference equation model for green crab popula-tion growth, competition and spread, and demonstrate that it yields appropriate spread rates for the two genotypes, based on historical data. Analysis of our model indicates that while harvesting efforts have the benefit of reduc-ing green crab density and slowing the spread rate of the two genotypes, elimination of the green crab is vir-tually impossible with harvesting alone. Accordingly, a green crab fishery would be sustainable. We also demon-strate that with harvesting and restocking, the competitive imbalance between the Northern and Southern green crab genotypes can be reversed. That is, a competitively infe-rior species can be used to control a competitively superior one.
Kanary L, Locke A, Watmough J, Chassé J, Bourque D, Nadeau A. Predicting larval dispersal of the vase tunicate Ciona intestinalis in a Prince Edward Island estuary using a matrix population model. Aquatic Invasions. 2011.
Abstract: Despite sporadic observations of the vase tunicate, Ciona intestinalis, on boats and mooring structures in Charlottetown Harbour, Prince Edward Island, the species has not established a population in the harbour nor dispersed the \~12 km downstream to Hillsborough Bay, an important source of blue mussel (Mytilus edulis) spat for the PEI aquaculture industry. A population matrix model used in conjunction with an oceanographic model suggests that advection of larvae from the harbour to the spat production area requires more than one or two generations, and the use of intermediate settlement nodes, such as navigational aids and aquaculture sites located in the upper part of Hillsborough Bay, as ‘stepping stones’. Maintaining potential settlement nodes in a tunicate-free condition could delay oceanographic dispersal of C. intestinalis within the estuary. According to observations of colonial tunicate dispersal in 2010, most likely originating from colonies established in the same locations where C. intestinalis inoculations have been detected, dispersal was occurring in the vicinity of one of the nodes identified by the model as priorities to be monitored for early detection of tunicate settlement, but had not yet reached the other node. A major finding is that the dispersal of solitary tunicates by oceanographic processes, often considered uncontrollable, is evidently amenable to management through monitoring and cleaning of the intermediate settlement nodes.
Kanary L. Spatial Dynamics of Ciona intestinalis Population Dispersal.; 2011.
Abstract: The vase tunicate Ciona intestinalis is wreaking havoc on the mussel farming industry in Prince Edward Island by fouling equipment and mussel socks used to harvest and grow the mussels. This invasive tunicate was detected recently in Charlottetown Harbour. If the tunicate persists in Charlottetown Harbour, larvae could disperse to and establish in down-current mussel spat growing leases in Nine Mile Creek. Mathematically modelling the population dispersal of the invasive in Hillsborough Bay, PEl, provides valuable information, such as species persistence, invasion propagation speed, maximum dispersal distance, and detection probability, to those managing the invasion. C. intestinalis prefer to settle on man-made substrate such as docks, boating equipment, mussel socks, which are the very items required to run a successful mussel farm. Factors affecting persistence on a substrate, such as eddy diffusion or advection, and settlement, reproduction, and mortality rates, can be manipulated in a mathematical model to provide insight on population dispersal patterns. A system of partial differential equations (PDEs) representing species dispersal in the bay provided persistence/extinction thresholds. The general conclusion was that a species with a low settlement rate will washout on small substrate with high diffusion and advection values. The same PDE model was analysed using a different method to provide the minimum propagation wave speeds in the bay so management can prepare for its eventual arrival. The PDE model was also used to determine the limits of dispersal. It is found that although direct dispersal from Charlottetown Harbour to Nine Mile Creek in one generation is unlikely, eventual dispersal by settling in stages is possible. Analysing a population matrix model, using advection data, leads to determining several key substrate areas, which should be removed or treated to hinder the invasion. A statistical model shows that roughly nine times out of ten, a reported adult tunicate is detected using the SCUBA method, which bodes well for early detection practices. In summary, the Charlottetown Harbour should support a C. intestinalis invasion because of its large domain size and the diffusion and advection values considered in the model. Thus, to discourage dispersal to Nine Mile Creek, regular monitoring of suitable substrate in the bay should be practiced, as well as removal or treatment of several key substrate areas. Monitoring in the mussel leases should be conducted using the SCUBA method; and monitoring of the navigational buoys, by removing and cleaning, should be practiced periodically. Keywords: partial differential equation, persistence, travelling waves, tunicate, aquatic invasive species, matrix model, Ciona intestinalis, rapid response / early detection, Prince Edward Island
Kanary L, Locke A, Watmough J. Evaluating the effectiveness of SCUBA-based visual searches for an invasive tunicate, Ciona intestinalis, in a Prince Edward Island estuary. Aquatic Invasions. 2010.
Abstract: Visual searches are a common method of detecting invasive species in coastal waters, but the statist ical properties of search methods have rarely been evaluated. Understanding the error rate (especially false negatives) and effective detection distance of searches can improve survey design, and quantify the uncertainty in risk assessments used to inform invasive species management efforts. An experiment using artificial tunicates (“decoys”) was conducted in Hillsborough Bay, Prince Edward Island, to determine the effectiveness of SCUBA divers conducting underwater visual searches for the vase tunicate, Ciona intestinalis (Linnaeus, 1767). Single decoys and clusters of three decoys, constructed from water -filled, ivory-coloured balloons 5-6 cm in length, were placed at a blue mussel, Mytilus edulis (Linnaeus, 1758), aquaculture site on buoys, lines and mussel socks. The probability of detecting tunicate decoys on a mussel sock in the experiment is 89.8% (±SD 7.1), known in this paper as a true positive. The probability of not detecting tunicate decoys actually placed on a mussel sock in the experiment is 10.2% (±SD 7.1), known in this paper as a false negative. Divers detected 79.2% (±SD 7.1) of single decoys and 94.0% (±11.4) of clusters. Divers were able to detect single decoys from a measured horizontal distance of 2.7 m (±0.8), and clusters from 2.8 m (±0.9). The typical detection distance for real C. intestinalis estimated by divers was, on average, 2.1 m (range 1 – 3 m), and tunicates of lengths ≥ 2.9 cm (range 1-4 cm) could be detected