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Bycatch of mid-trophic-level anadromous fishes that connect marine and freshwater ecosystems is a growing conservation concern. Anadromous alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) are important components of coastal freshwater and marine food webs, but have experienced dramatic declines in the abundances of spawning adults. Freshwater-focused restoration efforts have yielded few consistent signs of recovery, raising concerns that bycatch in Northwest Atlantic commercial fisheries may be negating these conservation actions. Using data from 15 microsatellites genotyped for baseline populations and bycatch, we conducted genetic stock identification to understand how bycatch was partitioned among previously identified regional genetic stocks. We then combined this information with fishery observer data to estimate genetic stock-specific bycatch mortality for the southern New England Atlantic herring fishery (2012-2013). Bycatch overall, but especially in the Atlantic herring fishery, was disproportionately assigned to the most severely depleted genetic stocks (alewife southern New England stock--70% of assignments; blueback herring mid-Atlantic stock--78% of assignments). These genetic stocks overlap in the region surrounding Long Island Sound, suggesting that bycatch taken from this area in recent years may be negatively impacting recovery efforts in this region. Our study suggests that mitigating bycatch on the southern New England fishing grounds may benefit recovery efforts for alewife and blueback herring genetic stocks that have experienced the greatest declines in spawning adult abundances. Les prises accessoires de poissons anadromes de niveaux trophiques intermediaires qui relient les ecosystemes marins aux ecosystemes d'eau douce sont de plus en plus preoccupantes en ce qui concerne la conservation. Si le gaspareau (Alosa pseudoharengus) anadrome et l'alose d'ete (Alosa aestivalis) sont des elements importants des reseaux trophiques marins et d'eau douce littoraux, ils ont connu des baisses considerables de l'abondance d'adultes reproducteurs. Les efforts de restauration axes sur les milieux d'eau douce ont produit peu d'indices de retablissement coherents, donnant a penser que ces efforts de conservation pourraient etre contrecarres par les prises accessoires dans les peches commerciales du nord-ouest de l'Atlantique. En utilisant les donnees de 15 microsatellites genotypes pour des populations de reference et des prises accessoires, nous avons identifie les stocks pour comprendre la repartition des prises accessoires parmi differents stocks genetiques regionaux deja identifies. Nous avons ensuite combine cette information a des donnees d'observation des peches pour estimer la mortalite des prises accessoires propre aux differents stocks genetiques pour la peche au hareng du sud de la Nouvelle-Angleterre (2012-2013). Les prises accessoires en general, mais particulierement dans la peche au hareng, etaient demesurement affectees aux stocks genetiques les plus decimes (70 % des affectations au stock de gaspareaux du sud de la Nouvelle-Angleterre; 78 % des affectations au stock medio-atlantique d'aloses d'ete). Ces stocks genetiques se chevauchent dans la region entourant le detroit de Long Island, donnant a penser que les prises accessoires prelevees dans cette region aucours des dernieres annees pourraient avoir un impact negatif sur les efforts de retablissement dans cette region. L'etude donne a penser que la reduction des prises accessoires dans les zones de peche du sud de la Nouvelle-Angleterre pourrait etre benefique pour les efforts de retablissement des stocks genetiques de gaspareaux et d'aloses d'ete ayant connu les baisses les plus importantes d'abondance d'adultes reproducteurs. [Traduit par la Redaction], Introduction The incidental catch of nontarget species in commercial fisheries (i.e., bycatch) represents a major threat to the health of marine ecosystems (Crowder and Murawski 1998; Chuenpagdee et al. 2003). [...]

A major challenge in conservation biology is the need to broadly prioritize conservation efforts when demographic data are limited. One method to address this challenge is to use population genetic data to define groups of populations linked by migration and then use demographic information from monitored populations to draw inferences about the status of unmonitored populations within those groups. We applied this method to anadromous alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), species for which long-term demographic data are limited. Recent decades have seen dramatic declines in these species, which are an important ecological component of coastal ecosystems and once represented an important fishery resource. Results show that most populations comprise genetically distinguishable units, which are nested geographically within genetically distinct clusters or stocks. We identified three distinct stocks in alewife and four stocks in blueback herring. Analysis of available time series data for spawning adult abundance and body size indicate declines across the US ranges of both species, with the most severe declines having occurred for populations belonging to the Southern New England and the Mid-Atlantic Stocks. While all alewife and blueback herring populations deserve conservation attention, those belonging to these genetic stocks warrant the highest conservation prioritization. [ABSTRACT FROM AUTHOR]