Top North American Finfish and Shellfish Fisheries by landed weight in Canada, the United States, and Mexico. Hashed bars indicate a combination of wild and aquacultured fisheries; filled bars indicate wild fisheries only; white bars with no fill indicate aquacultured fisheries only. Presence of microplastics investigations in the field or laboratory anywhere in the world is indicated by F (Field study), L (laboratory study), F/L (both field and laboratory studies), or I (Insufficient landings data). A star above the bar indicates that effects of microplastics have been studied.

Research is needed to determine effects and to assess the risk of microplastic ingestion and exposure on the commercially important species that are integral to the livelihoods and cultural histories of many North American communities. This synthesis of current evidence up until 01 March 2019 focuses on Canada, the U.S., and Mexico, though we acknowledge the importance of the fisheries and need for microplastic research in other countries and territories in this broad geographic region. We present the top commercial fishery species by North American country (Fig. 2 ; Supporting Information Appendix 1 ), display and describe which species have existing data on microplastics contamination and/or effects (Fig. 3 , Table 1 ), and identify priority research areas to better understand ecological and human health risks of microplastics in North American commercial fishery species.

Commercial fisheries and aquaculture in North America serve as cornerstones for many communities with deep roots in subsistence, recreational, and commercial fishing. These sectors support cultural practices and provide widespread employment throughout the continent (FAO 2018 ). Commercially harvested species are facing a myriad of threats in the Anthropocene, ranging from increasing ocean temperatures to modified habitats, pollution, and marine debris (Halpern et al. 2015 ; Lusher 2015 ; Hare et al. 2016 ; DeCourten et al. 2019 ). Interactions with marine debris are deeply problematic for marine species such as turtles, seabirds, marine mammals, and fishes (Wilcox et al. 2016 , 2018 ), with entanglement and ingestion documented to cause harm at the individual and possibly population levels (Kühn et al. 2015 ). Plastic marine debris poses varied threats to individual organisms as well as entire food webs based on size, chemical composition, and bioavailability (Fig. 1 ; Gall and Thompson 2015 ). Microplastics, synthetic polymeric particles or fibers 0.0001–5 mm in length are an emerging area of study because they are ingested and respired by hundreds of different marine and aquatic species (Rochman et al. 2016 ). Numerous studies have documented effects of microplastic internalization ranging from sublethal responses such as reduced fecundity, altered growth, and increased stress to mortality at higher particle concentrations (e.g., Rochman et al. 2013 , 2014 ; Mazurais et al. 2015 ; Critchell and Hoogenboom 2018 ).

As global seafood consumption rises, it is important to understand the mechanisms by which fisheries are affected by microplastic pollution. A growing body of literature describes the occurrence and effects of microplastics in commercial species, primarily from Europe, Asia, and South America; however, there are far fewer studies conducted in North America. In this article, we review the evidence available for the presence and effects of microplastics on commercially valuable fishery species of North America and possible consequences of human consumption. We identify key priorities for future research on this topic including geographic and taxonomic representativeness; physiological, organismal, and population level effects; microplastics as multiple stressors; human health risks; and standardization of field and lab protocols.

Like finfish, shellfish (including crustaceans, bivalves, and other molluscs) are important players in North American coastal ecosystems, cultures, economies, and diets. Dozens of species are harvested from the wild in Canada, the U.S., and Mexico (Supporting Information Appendix 1 ). In Canada, crabs ( Cancer magister , Chionoecetes opilio , C. bairdi ) and lobster ( Homarus americanus ) comprise the bulk of wild‐caught shellfish production, totaling roughly 0.10 Mt landed for each respective fishery in 2017 (Fig. 2 ; Supporting Information Appendix 1 ; Fisheries and Oceans Canada 2018). Wild Atlantic prawn ( Pandalus borealis ), a coldwater shrimp, has historically been one of the most important commercial harvests off the east coast of Canada, however as of 2018, NOAA reports this fishery collapsed (National Marine Fisheries Service 2018a , b ). Along the Gulf of Mexico, there are 49 officially recognized shellfish species harvested, with 16 species collected from U.S. waters, and 46 harvested from Mexican waters (Tunnell 2017 ). In the U.S., shrimp, squid, crabs ( Cancer magister , Callinectes sapidus , Chionoecetes opilio , C. bairdi ), and lobster ( Homarus americanus ) were the highest‐volume, highest‐value fisheries in 2017 (Fig. 2 ; Supporting Information Appendix 1 ; National Marine Fisheries Service 2018a , b ). Shrimp, oysters, squid, and crab were the most significant shellfisheries in Mexico in 2014, the most recent year for which landings data are available (Supporting Information Appendix 1 ), though differences between wild‐caught and farmed fisheries are difficult to parse out (Melgoza‐Rocha et al. 2018 ). Fisheries along the Gulf of Mexico coastline continue to fluctuate in response to natural and anthropogenic distrurbances (Tunnell 2017 ) and fishery data are likely underreported (Finkbeiner and Basurto 2015 ). Overall, the continued strength of these wild fisheries is critical to the economies of all three countries, thus emerging anthropogenic effects such as those presented by microplastics are of considerable concern. While this paper does not focus on wild fisheries for subsistence by tribal and other entities, it is also important to consider the importance of these wild resources through this lens. Based on these data, the relevant species for studying microplastics in North American commercial fisheries vary regionally but with some species groups in common—an important consideration when targeting and designing future studies.

Though North America is not a top global producer of aquacultured seafood, the region is a significant contributor to global marine finfish landings (Supporting Information Appendix 1 ; FAO 2018 ). Among the three countries, the U.S. has the highest landings and is ranked 3 rd globally for total marine capture, having produced 3.96 Mt in 2017. Canada reported 0.43 Mt in commercial finfish landings for 2017 with Pacific salmon ( Oncorhynchus spp.), herring ( Clupea spp.), hake ( Merluccius spp.), redfish ( Sebastes spp.), and cod the most frequently landed (Fisheries and Oceans Canada 2018). In the U.S., the top species by landed weight were Alaskan pollock ( Gadus chalcogrammus ), menhaden ( Brevoortia spp.), Pacific salmon ( Oncorhynchus spp.), hake, and cod ( Gadus spp.; see Fig. 2 , Supporting Information Appendix 1 ; National Marine Fisheries Service 2018a , b ). Just over 1.0 Mt of commercial finfish were landed in Mexico where Pacific sardines ( Sardinops sagax ), tuna (various spp.), tilapia (various spp.), anchoveta ( Cetengraulis mysticetus ), and carp (various spp.) were among the most captured in 2014 (Melgoza‐Rocha et al. 2018 ; most recent data available).

No crustacean aquaculture farms currently exist in Canada; however, across the U.S. and Mexico, brown, white, and pink shrimp ( Farfantepenaeus aztecus , Litopenaeus setiferus , Farfantepenaeus duorarum ) are the primary crustaceans farmed (FAO 2018 ). Most of this industry is located on the Gulf Coast of Mexico, primarily in Louisiana, Alabama, and Texas in the U.S. and into the Gulf Coast of Mexico. Mexico's shrimp aquaculture recorded 0.056 Mt in 2003 (National Aquaculture Sector Overview 2018 ). Although aquacultured species represent a relatively small fraction of seafood produced and consumed in North America, a substantial presence as well as predictions of increased production makes this market important for the consideration of potential microplastic effects.

The primary species used in shellfish aquaculture varies by North American country (Supporting Information Appendix 1 ). In Canada, the most valuable cultured shellfish fisheries on both the Atlantic and Pacific coasts are mussels ( Mytilus edulis) , oysters ( Crassostrea virginica , C. gigas ), clams (Manila clam Venerupis philippinarum , soft‐shell clam Mya arenaria , geoduck Panopea generosa , quahog Mercenaria mercenaria , littleneck clam Protothaca staminea , varnish clam Nuttallia obscurata ), and scallops (Supporting Information Appendix 1 ). In 2017, while mussels were the largest farmed shellfish fishery by landing weight in Canada (0.024 Mt), oysters were the most valuable fishery at $33.93 million USD ($45.12 million CAD; Supporting Information Appendix 1 ). In 2016, the year with the most recent U.S. aquaculture data, U.S. shellfish aquaculture yielded 0.017 Mt of oysters ($192 million USD), 0.005 Mt of clams ($138 million USD), and 0.002 Mt of shrimp ($10 million USD; National Marine Fisheries Service 2018a , b ). In Mexico, farmed bivalve species include the blue mussel, hard clams, oysters ( C. virginica , C. gigas , C. corteziensis , Pteria sterna , Pinctada mazatlanica ), and scallops. The Eastern oyster is the most heavily cultured bivalve in the Gulf of Mexico and is sold for both human consumption and adornments using its pearls and shells (National Aquaculture Sector Overview 2018 ; Tunnell 2017 ).

Over 50% of global seafood consumption is derived from aquaculture production, with an increase to 62% of global consumption predicted by 2030 (World Bank 2013 ; FAO 2018 ). North America is currently a minor player on this global aquaculture stage, accounting for less than 1% of global production in 2014, a contribution that has steadily declined over the last two decades (FAO 2016 ), but with a forecasted increase in the coming decades. Aquaculture in North America is dominated by finfish production with a smaller segment dedicated to production of bivalve molluscan shellfish, predominantly oyster, clam, and mussel species (Fig. 2 ; Supporting Information Appendix 1 ). Atlantic salmon ( Salmo salar ) and rainbow trout ( Oncorhynchus mykiss ) are the chief finfish species farmed in Canada (FAO 2018 ) whereas Channel catfish ( Ictalurus punctatus ), rainbow trout, and Atlantic salmon are the leading finfish produced by U.S. aquaculture (National Marine Fisheries Service 2018a , b ). In 2014, finfish aquaculture in Mexico was dominated by production of tilapia, carp, and trout varieties (Fig. 2 ; Supporting Information Appendix 1 ; Melgoza‐Rocha et al. 2018 ).

As of 2016, 88% of global aquaculture and fisheries production was utilized for human consumption (FAO 2018 ). Commercial fisheries in North America are no exception, with recent estimates for annual per capita seafood consumption at 22.6 kg, 7.3 kg, and 3.6 kg for Canada, the United States (U.S.), and Mexico, respectively (FAO 2014 ; Cantoral et al. 2017 ; National Marine Fisheries Service 2018a , b ). In 2016, Canadian commercial marine and freshwater fisheries landed 0.88 million metric tons (1 million metric tons = Mt) for a total value of $2.56 billion USD ($3.37 billion CAD), with aquaculture accounting for an additional $1.02 billion USD ($1.34 billion CAD). The industry labor force in Canada includes 44,000 commercial fish harvesters and crew, 3,300 individuals employed by the aquaculture industry, and an additional 28,700 individuals in the seafood product preparation and packaging sectors (DFO 2018 ). U.S. fisheries landings for the same year were 4.49 Mt and exceeded $5.4 billion USD in value (National Marine Fisheries Service 2017 ). In 2016, these efforts were supported by over 1.2 million jobs in the U.S. (National Marine Fisheries Service 2018a , b ). Between 2006 and 2014, the coastal states of Mexico produced 1.3 Mt of fish and seafood per year (85% from wild caught fishery landings; 15% from aquaculture), with an average annual economic value of $890 million USD ($17 billion MXN), and supported roughly 238,000 and 56,000 jobs, respectively, in the fishing and aquaculture sectors (Melgoza‐Rocha et al. 2018 ). These numbers highlight the economic and cultural importance of this sector. The use of commercial seafood for fresh, frozen, canned, and cured products is integral to the economies of all three North American countries and the reliance on commercial fisheries, both wild‐caught and aquacultured, for protein is predicted to increase substantially over the next few decades (World Bank 2013 ).

Marine microplastics: A brief review

Marine anthropogenic debris, primarily in the form of plastics, is ubiquitous and persistent, and comprises up to 95% of all waste in global oceans and on beaches (Andrady 2011; Eriksen et al. 2014; Galgani et al. 2015). The amount of plastic entering the marine environment continues to increase annually and it is estimated that in 2010 alone, 4.8–12.7 Mt of plastic ended up as marine litter, representing 1.7–4.6% of the total plastic waste generated in 192 coastal countries (Jambeck et al. 2015). Microplastics, 0.0001–5 mm in size, have been documented throughout the water column, in surface waters, sediments, and in marine organisms and are therefore a global threat to marine ecosystems (Barnes et al. 2009; Avio et al. 2017). Although widespread, distribution of microplastics in coastal and marine environments is unpredictable and patchy because meteorological, atmospheric, coastal, and tidal processes all contribute to the movement, dispersal, and accumulation of these largely buoyant particles (Foekema et al. 2013). However, the microplastics problem is particularly pronounced in coastal zones due to their proximity to terrestrial inputs, tidal processes that provide favorable conditions for debris accumulation (Ryan et al. 2009; Weinstein et al. 2016; Gray et al. 2018), wave action, and UV light exposure that collectively promote fragmentation (Andrady 2011). The risks of microplastic exposure to coastal fisheries and aquaculture in North America are not well defined.

Not only is plastic found widely in the marine environment, it is also ingested by hundreds of species around the world, spanning freshwater, coastal, pelagic, demersal, benthic, as well as deep‐sea environments (Rochman et al. 2015; Alomar and Deudero 2017; Jamieson et al. 2019). A 2015 meta‐analysis by Gall and Thompson indicated that over 690 species have reported encounters with marine debris through entanglement and ingestion, with 92% of those encounters involving plastic. Over 220 species of marine organisms, ranging from microscopic zooplankton to bivalves, fish, marine mammals, sea turtles, sharks, seabirds, and a host of other marine‐associated species, have been documented to ingest plastics (Lusher et al. 2017). The majority of microplastic pollution research in North America has sought to determine environmental concentrations of microplastics in lakes, rivers, estuaries, and sediments, with recent investigations of municipal wastewater treatment plants (WWTPs) as potential avenues for microplastics to enter aquatic ecosystems (Auta et al. 2017; Gies et al. 2018). For example, Mason et al. (2016) reported the average concentration of microplastics in WWTP effluent across the United States as 0.05 ± 0.024 particles L−1. Freshwater ecosystems in North America were also found to have an abundance of microplastics. Eriksen et al. (2013) reported microplastic concentrations in the Great Lakes of: 1277–12,645 particles km−2 in Lake Superior, 0–6541 particles km−2 in Lake Huron, and 4686–466,305 particles km−2 in Lake Erie. Microplastics are also present in North American lake sediments with 140–980 items kg−1 dry sediment recorded for Lake Ontario (Ballent et al. 2016). Microplastic concentrations in North American river water and sediments have been reported across a wide range. For example, the San Gabriel and Los Angeles Rivers of California contained 411 particles m−3 and 12,932 particles m−3 of water, respectively (Moore et al. 2011). Notably, microplastic levels in the waters of the North Shore Channel in Chicago, Illinois, U.S., downstream from a WWTP, were measured at 17.93 ± 11.05 particles m−3 (McCormik et al.2014; Shahul Hamid et al. 2018) and in the St. Lawrence River in Canada were 13,832 ± 13,677 particles m−2 of sediment (Castañeda et al. 2014). These data provide evidence that waterways act as both sinks of some microplastic pollution as well as sources of microplastic pollution to marine systems.

Below, we review existing data on microplastics in North American fisheries species current to 01 March 2019, and outline the needs and future directions for the study of occurrence and effects of microplastics in commercially harvested finfish, bivalves, and crustaceans in this part of the world. We offer suggestions for future laboratory and field studies related to commercial fisheries in Canada, the U.S., and Mexico.

Ecological prevalence and effects The primary route of organismal microplastic exposure occurs via ingestion of microplastics mistaken for natural prey items (Lusher 2015), or ingestion of contaminated prey items (Nelms et al. 2018), though both finfish and shellfish can also passively uptake microplastics through respiration and via the gills (Watts et al. 2015). Consumed microplastics can transfer across trophic levels and may bioaccumulate in predators (Farrell and Nelson 2013; Setälä et al. 2014). Plastic materials identified in the digestive tracts of marine organisms include fibers, foams, films, and fragments with recorded chemical signatures of cellophane, high density polyethylene (HDPE), low density polyethylene (LDPE), polyethylene terephthalate (PET, PETE), nylon (PA), polypropylene (PP), polymethylmethacrylate (PMMA), polyurethane (PU, PUR), polystyrene (PS), among others determined by various spectroscopic techniques such as Fourier‐transform infrared (FTIR) and Raman spectroscopy (Hidalgo‐Ruz et al. 2012; Wagner et al. 2017; Pinto da Costa et al. 2019). Microfibers are the most prevalent category of microplastics ingested by marine fishes, crustaceans, and bivalves, typically representing more than 90% of plastics ingested (Mizraji et al. 2017), with microplastic fragments, foams, and films representing a smaller proportion (Jabeen et al. 2017). Additives and monomers, including bisphenol A (BPA), organotoxins, and phthalates, with established biologically harmful properties such as reproductive toxicity, mutagenicity, and carcinogenicity, are used to manufacture plastics (Teuten et al. 2009). If microplastics are ingested, these compounds can be released from the polymer and absorbed by predators (Browne et al. 2008, 2013). In addition to containing additives, plastics also adsorb harmful hydrophobic persistent organic pollutants (POPs) such as dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls, polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers, and dioxins, among others (Rios et al. 2007; Bakir et al. 2014; Gallo et al. 2018). Because of their high surface area to volume ratio and hydrophobic nature, microplastics are known to sorb hydrophobic organic pollutants in concentrations up to 1 million times greater than surrounding waters (Mato et al. 2001). Under physiological conditions, these pollutants may desorb into the digestive tracts of animal predators when ingested. The ability of plastics to sorb to chemicals that can become bioavailable is a concern attributed to microplastic consumption, although studies are ongoing to determine whether leaching from ingested plastics significantly increases contaminant burden. However, the endocrine disrupting properties of these hydrophobic and persistent chemicals in wildlife are well documented, as well as the ability of such chemicals to cause sublethal effects on growth, reproduction, and behavior at very low concentrations (e.g., ng L−1) (reviewed in Colborn and Thayer 2000; Brander 2013). As such, the leaching of even small amounts of these pollutants from ingested plastic may pose an additional hazard to marine organisms. Furthermore, internal migration of plastic particles has been documented in fish and crabs in laboratory studies that report smaller microparticles translocated internally to the circulatory system and tissues (e.g., liver, hepatopancreas) in a range of taxa (Browne et al. 2008; Avio et al. 2015; Brennecke et al. 2015). In the model zebrafish, microplastics can be maternally transferred to eggs (Pitt et al. 2018). Translocation of microplastics may make leaching of associated chemicals more likely. Marine species, including those harvested for commercial purposes, may therefore be ingesting both plastic debris and a cocktail of associated contaminants (Rochman et al. 2015). Laboratory studies have demonstrated that continuous exposure to contaminated plastics can lead to accumulation of plastic‐associated pollutants in fish tissue in as little as 21 d (Rochman et al. 2013; Wardrop et al. 2016).