Rishi Sharma - Academia.edu (original) (raw)

Papers by Rishi Sharma

Fish and Fisheries, 2021

Implementation of the United Nations Sustainable Development Goals requires assessments of the gl... more Implementation of the United Nations Sustainable Development Goals requires assessments of the global state of fish populations. While we have reliable estimates of stock status for fish populations accounting for approximately half of recent global catch, our knowledge of the state of the majority of the world's “unassessed” fish stocks remains highly uncertain. Numerous publications have produced estimates of the global status of these unassessed fisheries, but limited quantity and quality of data along with methodological differences have produced counterintuitive and conflicting results. Here, we show that despite numerous efforts, our understanding of the status of global fish stocks remains incomplete, even when new sources of broadly available data are added. Estimates of fish populations based primarily on catch histories on average performed 25% better than a random guess. But, on average, these methods assigned fisheries to the wrong FAO status category 57% of the time...

ICES Journal of Marine Science, 2017

The article examines factors related to the decline and rebuilding of billfish stocks in the Atla... more The article examines factors related to the decline and rebuilding of billfish stocks in the Atlantic and Indian oceans. Longline effort has declined over the last 10–15 years in both oceans. This decline in fishing pressure has led to the recovery of some stocks, but some species that are caught incidentally in industrial longline fisheries remain overexploited. Using a simple moving average technique on fishing mortality trajectories, we estimated a threshold effort size of 240 million hooks for the Atlantic Ocean and 364 million hooks for the Indian Ocean where stocks start experiencing overfishing. In addition, we highlight differences in the economic characteristics of the major fleets catching billfish in the two oceans and discuss how this may be associated with differences in management, enforcement, and stock rebuilding.

Aquatic Conservation: Marine and Freshwater Ecosystems, 2014

1. Two distinct populations of resident killer whales (Orcinus orca) in the northeastern Pacific ... more 1. Two distinct populations of resident killer whales (Orcinus orca) in the northeastern Pacific Ocean have been listed in Canada and the USA as being of conservation concern. One of the major threats recognized for these two populations is nutritional stress associated with prey abundance levels and availability. 2. The predominance of chinook salmon (Oncorhynchus tshawytscha) in the summer diets of both killer whale populations has been shown by recent studies, and correlations between indices of chinook salmon abundance and resident killer whale (RKW) vital rates have generated hypotheses about the potential for chinook salmon abundance to limit RKW population dynamics. 3. This study merges statistical inference derived from linkages between RKW vital rates (survival probability and fecundity rates) and chinook salmon abundance with demographic perturbation analysis and population viability analysis to address some of the pressing questions that have recently engaged the efforts of scientists and managers interested in: (1) the role of chinook salmon abundance in the population dynamics of RKW; and (2) how RKW population viability is expected to respond to changes in chinook mortality owing to harvest. 4. Numerous interactions between the abundance of chinook salmon aggregates and RKW vital rates were found and deemed to result from predator-prey dynamics. However, the results of this present analysis also indicated that the effects of these interactions on RKW population growth and viability are relatively small and/or uncertain and in need of further research. 5. Other factors (genetic, environmental and/or anthropogenic) could be at play limiting RKW population growth and possibly masking and confounding the detection of stronger interactions between RKW vital rates and chinook salmon abundance. Given the current state of information, it is highly uncertain whether the allocation of chinook salmon resources for RKW would be an effective management action in RKW recovery plans.

Canadian Journal of Fisheries and Aquatic Sciences, 2001

We assembled data on coho salmon (Oncorhynchus kisutch) from 14 streams in western Washington, in... more We assembled data on coho salmon (Oncorhynchus kisutch) from 14 streams in western Washington, including annual smolt counts and annual escapement, either as absolute counts or as an index. We also compiled data on large woody debris (number•km-1 of stream), road densities in the watersheds (km road•km-2), gradient of the streams (%), valley slope adjacent to the stream (%), drainage area in the watershed (km 2), and pool, pond, and lake areas (m 2 •km-1). We explored the relationships between habitat variables and two measures of coho production, the maximum production of smolts in the stream (capacity) and the maximum smolts/spawner (productivity). Using the 11 streams with pool and pond counts, we found that pool and pond densities served as good predictors of smolt density (r 2 = 0.85 for pools and 0.68 for ponds, independently). Pools produced 0.39 smolts•m-2 and ponds produced 0.07 smolts•m-2 in the multiple regression fit, accounting for 92% of the residual error. We also found that lower valley slopes, lower road densities, and lower stream gradients were correlated with higher smolt density. Résumé : Nous avons rassemblé des données sur le Saumon coho (Oncorhynchus kisutch) de 14 cours d'eau du Washington occidental, entre autres des recensements annuels de saumoneaux et des échappées annuelles, tant en valeurs absolues qu'en indices relatifs. Nous avons aussi compilé des informations sur la présence de débris ligneux de grande taille (nombre•km-1 de cours d'eau), sur la densité des routes dans le bassin versant (km route•km-2), la pente du cours d'eau (%), la pente de la vallée adjacente au cours d'eau (%), la surface de drainage dans le bassin versant (km 2), ainsi que la surface des profonds, des étangs et des lacs (m 2 •km-1). Nous avons alors exploré la relation entre les variables de l'habitat et deux mesures de production des saumons, la production maximale de saumoneaux dans le cours d'eau (capacité) et le maximum de saumoneaux par géniteur (productivité). Dans les 11 cours d'eau pour lesquels nous avions des données sur les profonds et les étangs, les densités des profonds et des étangs se sont avérées être de bonnes variables prédictives de la densité des saumoneaux (r 2 = 0,85 pour les profonds et 0,68 pour les étangs, indépendamment). Une régression multiple qui explique 92% de l'erreur résiduelle indique que les profonds produisent 0,39 saumoneau•m-2 et les étangs 0,07 saumoneau•m-2. Les valeurs plus faibles de pentes des vallées, de densités des routes et de pentes des cours d'eau sont liées aux densités de saumoneaux plus élevées.

A stock assessment for albacore tuna in the Indian Ocean was developed using Stock Synthesis vers... more A stock assessment for albacore tuna in the Indian Ocean was developed using Stock Synthesis version 3. The model included catch data from 1952 to 2012. A Stock Synthesis assessment was run in 2012, and this assessment makes a number of changes and documents their effects on the results. Size data were analyzed and the spatial structure of the fisheries was changed to improve the consistency of sizes within the fisheries. Sensitivity runs were carried out with alternative parameters for natural mortality, growth, selectivity, steepness, and spatial structure. Alternative values of biological parameters were explored, given that the different tuna-RFMOs use different assumptions in their stock assessments, in some cases with little evidence, and there are substantial data gaps for Indian Ocean albacore. We examined conflicts among different sources of data and assumptions by down-weighting the different data sources. The sensitivity of management advice to the above explorations was used to identify priority areas for further research. The inferred structural uncertainty, including interactions, was included in the management advice. The assessment incorporates projections for 10 years and provides a Kobe II Strategy Matrix decision table. The preliminary stock status using a reference base case assessment contradicts results obtained in 2012, indicating that the stocks is in a healthy status and is not experiencing overfishing or is in an overfished status. The only scenario that contradicts this conclusion is a low steepness value, with a very low natural mortality rate that is highly unlikely given the life history of Albacore.

An Indian Ocean swordfish (Xiphias gladius) stock assessment using Stock Synthesis 3 (SS3) softwa... more An Indian Ocean swordfish (Xiphias gladius) stock assessment using Stock Synthesis 3 (SS3) software is described. The approach uses a highly disaggregated model to integrate several sources of fisheries data and biological research into a unified framework. The model used is updated from the analysis conducted in 2011. Rather than use a fairly complex grid as used in 2011, the model examined this year key uncertainties, namely growth, natural mortality, steepness and weighting of the length composition data as opposed to the CPUE survey data (2 growth curves with 2 natural mortality vectors that correspond to the growth curves from a biological basis (total of 2 choices), 3 steepness values, and two weighting alternatives of data, and examining once CPUE series scenario that is equally weighted across all series, and one that only examines the Japanese CPUE series, with the EU fleets representing the SW Region). The implications of 10 years of projections over a ranged of constant c...

We used stock–recruit analyses to determine the effect of Priest Rapids Dam operations on the pro... more We used stock–recruit analyses to determine the effect of Priest Rapids Dam operations on the productivity of the Hanford Reach fall Chinook salmon population for brood years (BY) 1975–2004. Productivity was defined as the number of pre-smolts (recruits) produced from a BY divided by the egg escapement (stock) present to produce that brood. This definition of productivity ensured that only the life stages expected to be directly affected by Priest Rapids Dam operations in the Hanford Reach were considered. The Ricker model was fit to the data, and residuals were used to identify BY of above- and below-average pre-smolt/egg production. In addition, analysis of covariance (ANCOVA) was used to determine whether a difference existed in the productivity parameter (Ricker α) between pre- and post-Vernita Bar Settlement Agreement (VBSA) periods. Pre-smolt/egg estimates were regressed against a host of dam operation and environmental variables to identify variables that may have affected pr...

Transactions of the American Fisheries Society, 2012

For salmon populations in the Columbia River basin, many of which are listed under the U.S. Endan... more For salmon populations in the Columbia River basin, many of which are listed under the U.S. Endangered Species Act of 1973, reliable estimation of the proportion of hatchery-origin spawners in spawning areas (p) is needed to make inferences about their status and potential for interbreeding with wild-origin adults, which may reduce the genetic fitness of subsequent generations. Despite its importance,

North American Journal of Fisheries Management, 2009

We examined three types of models for preseason forecasting of the abundance of Queets River coho... more We examined three types of models for preseason forecasting of the abundance of Queets River coho salmon Oncorhynchus kisutch: (1) a simple model in which estimates of smolt production are multiplied by projected marine survival rates, (2) a Ricker spawner-recruitment model, and (3) a regression model relating log-transformed adult recruitment to smolt production. Each type of model was formulated with and without environmental variables that influence production and survival. We attempted to use a nonparametric generalized additive model (GAM) to guide the selection of the environmental variables and the form of the regression model. The GAM model was derived through a stepwise selection strategy based on the Akaike information criterion. Parametric approximate models were developed for each selected GAM model, and their performance was compared with postseason estimates of abundance using three criteria: the mean absolute percentage error, the largest absolute percentage error, and the probability of being included in the 90% prediction interval. This paper shows that the GAM approach is useful in constructing forecasting models by identifying promising relationships with predictor variables and improving abundance forecasts through the incorporation of environmental variables.

North American Journal of Fisheries Management, 2005

Fisheries Research, 2012

Forecasts of returns are used to determine appropriate levels for ocean and in-river harvests of ... more Forecasts of returns are used to determine appropriate levels for ocean and in-river harvests of northeast Pacific fall Chinook salmon (Oncorhynchus tshawytscha). The current preseason forecasts are made by February, six months before fish arrive at natal rivers. As such, they do not capture ecosystem changes that occur after February. We incorporated catch and effort data from the Alaska summer commercial fishery to detect unusual ecosystem variability in fish return years and to update forecasts during the ocean fishery season. In addition, the traditional model using the ordinary regression unnecessarily has an intercept term, which often leads to unusual over-forecasts. Further there are concerns about autocorrelation in Chinook salmon returns. Finally the current practice does not provide information about the uncertainty inherent in the forecasts. To address these issues, we developed new forecast models and compared them with the traditional method. The models considered are: I, traditional preseason forecasts; II, autoregressive preseason forecasts without intercept term; III, ocean fishery real-time forecasts; IV, integrated forecasts from models I and III; and V, integrated forecasts from models II and III. We validated our models, using data from three Columbia River stocks [Upriver Bright (URB), Lower River Wild (LRW), and Mid-Columbia Bright (MCB)], and from two Canadian stocks [Fraser River Lates (FRL) and West Coast Vancouver Island (WCVI)].

Fisheries Oceanography, 2013

Pacific Northwest Chinook, Oncorhynchus tshawytscha, have exhibited a high degree of variability ... more Pacific Northwest Chinook, Oncorhynchus tshawytscha, have exhibited a high degree of variability in smoltto-adult survival over the past three decades. This variability is summarized for 22 Pacific Northwest stocks and analyzed using generalized linear modeling techniques. Results indicate that survival can be grouped into eight distinct regional clusters: (1) Alaska, Northern BC and North Georgia Strait; (2) Georgia Strait; (3) Lower Fraser River and West Coast Vancouver Island; (4) Puget Sound and Hood Canal; (5) Lower Columbia Tules; (6) Columbia Upriver Brights, Willamette and Cowlitz; (7) Oregon and Washington Coastal; and (8) Klamath River and Columbia River Summers. Further analysis for stocks within each of the eight regions indicates that local ocean conditions following the outmigration of smolts from freshwater to marine areas had a significant effect on survival for the majority of the stock groups analyzed. Our analyses of the data indicate that Pacific Northwest Chinook survival covaries on a spatial scale of 350-450 km. Lagged time series models are presented that link large-scale tropical Pacific conditions, intermediate-basin scale northeastern Pacific conditions, and local sea surface temperatures to survival of Pacific Northwest stocks.

Fisheries Management and Ecology, 2010

Escapement goals for Chinook salmon, Oncorhynchus tshawytscha (Walbaum), populations tend to be h... more Escapement goals for Chinook salmon, Oncorhynchus tshawytscha (Walbaum), populations tend to be highly uncertain due to variability in, and in some cases complete absence of, spawner-recruit data. A previous study of 25 populations from Oregon to Alaska demonstrated that watershed size is a good predictor of unfished equilibrium population size. Here this relationship is further developed by evaluating a series of Bayesian hierarchical models of increasing complexity. The model that performed best included a temporal random walk to account for patterns in the spawner-recruit residuals and life history-specific distributions for the productivity parameter.