The extent of occurrence of Scomberomorus concolor is estimated to have reduced by more than 80%, based on both historical and new information. Prior to 1961 there were records of this species along coastal southern California, however since the 1980s there is strong evidence that it is now restricted to the northern and eastern central coast of the Gulf of California. A greater than 80% reduction in the population has been inferred over the past 40 years based both on the reduction in range and from the current levels of exploitation. Although the majority of range reduction appears to have occurred before the time window of three generation lengths (12 years), there have been relatively few sightings of this species over the past 30 years, and no confirmed sightings over the past 10 years (3 generation lengths). However, population data in general have historically been mixed with its popular fishery sister species Scomberomorus sierra, which may partially explain the lack of confirmed sightings.

Scomberomorus concolor co-occurs with two other threatened species, the Vaquita and the Totoaba, within the marine Biosphere Reserve in the upper Gulf of California. However, it is known to seasonally migrate outside of this MPA from October to May, where an analysis by the Mexican Instituto Nacional de Pesca in 2002 showed that fishing effort outside of the MPA was expected to lead to a decline of at least 40% within the next 10 years. Given its depth range of 0–15 m and an assumed current distribution limited to the northern and eastern central coast of the Gulf of California, this species has an estimated area of occupancy of less than 4,500 km2. However, given current fishing pressure outside of the MPA, and the lack of confirmed records of this species over the past decade, this species may have an even smaller distribution than assumed. It is therefore assessed as Near Threatened (nearly meets criterion B).

Monterey Spanish Mackerel are endemic to the Eastern Pacific. Historically, this species likely had a continuous distribution from Monterey Bay, California, around Baja California and throughout the Gulf of California. They were caught commercially in the 1870s and 1880s in Monterey Bay, California (Lockington 1879, Goode 1884). The initial diminution of range began between 1880 and 1920, perhaps associated with gradual reduction in water temperature along the California coast (Hubbs 1948, Fitch and Flechsig 1949). However, there have only been 10 historic records from the California coast (Fitch and Flechsig 1949), and its occurrence on the west shore of the Gulf of California is extremely rare, with only a few confirmed records over the past 40 years.

This species was considered abundant in the Gulf of California in the 1970s (Collette and Russo 1985) and was observed in Guaymas in the early 1980s (L. Findley, pers. comm. 2022). However, the present distribution of this species is now limited to the central and northern part of the Gulf of California. Additionally, over the last 30 years, very few specimens have even been recorded in this restricted area, with the most recent records from Loreto in the lower Gulf of California recorded more than 30 years ago in 1993 (Collette and Graves, 2019) and from the central and northern Gulf of California recorded more than 15 years ago in 2005–2008 (Magallon-Gayon et al. 2016, Dominguez-Lopez et al. 2015). Given its depth range of 0–15 m and a distribution restricted to the northern and eastern coast of the Gulf of California, it has an estimated area of occupancy of less than 4,500 km2. However, given that there have been very few records of this species over the past few decades, this species may have an even smaller distribution than assumed.

The Monterey Spanish Mackerel was caught commercially in the 1870s and 1880s in Monterrey Bay, California, and was considered abundant in the Gulf of California in the 1970s (Collette and Russo 1985). It is among the top four species taken by small-scale fishing operations inside the upper Gulf of California Biosphere Reserve (Erisman et al. 2015). Genetic analyses support the existence of a single panmictic population in the Gulf of California (Magallón-Gaysome et al. 2016).

No catches have been reported to FAO for Scomberomorus concolor, but there is a large reported catch from Mexico of its sister species of Spanish mackerel, the Pacific Sierra (Scomberomorus sierra), which was 6,919 to 14,573 metric tons from 2010 to 2019 (FAO 2022). Some of this catch from the Gulf of California is likely Scomberomorus concolor because part of the catches are combined, and therefore it is not possible to determine a population trend for this species. However, there are no current management measures in place for its sister species (Domingues-Lopez et al. 2010, Domingues-Lopez et al. 2015), which is likely having severe effects on the remnant of the S. concolor population. A study by the Mexican Instituto Nacional de Pesca in 2002 showed that fishing effort outside of protected areas was expected to lead to a decline of at least 40% within the next 10 years.

Intense fishing pressure on spawning aggregations that are predictable in time and space appear to have led to rapid declines, and some studies have estimated that this species may be at high risk of collapse (Quiñónez-Velazquez and Montemayor-Lopez 2002), or near to its maximum level of exploitation (Valdovinos-Jacobo 2006). However, a genetic study (Magallón-Gayón et al. 2016) of individuals collected between 2005 and 2008 along the eastern central coast of the Gulf of California estimated an effective population size (Ne) of Monterey Spanish Mackerel as a single population with an Ne value of 3056, which was not thought to correspond to a population at risk of collapse at that time.

Monterey Spanish Mackerel are residents of the coastal pelagic environment of the upper Gulf the year round (Erisman et al 2015). There is a single homogeneous population in the Gulf that moves seasonally to spawn and feed (Dominguez-López et al. 2015). Their biology is poorly known. They occur along the upper east coast of the Gulf of California in the fall months in shallow estuaries; spawning occurs in late spring and early summer. It may be a colder water fish than S. sierra, retreating to deep waters in summer. It spawns and swims with S. sierra. It moves from a feeding zone in the central Gulf of California near Guaymas from October to May, to a spawning zone in the northern Gulf of California from May to August (Valdovino Jacobo et al. 2006, Dominguez-Lopez et al. 2015). The reproductive season for Monterey Spanish Mackerel begins in April, peaks from April through July, and ceases by September (Erisman et al. 2015). The best place to currently find this species is in the spring around Isla San Jorge, 50 km south of Puerto Penasco.

Monterey Spanish Mackerel feed on euphausiid shrimps and clupeids (Valdovinos Jacobo et al. 2006). In the winter when cooler conditions predominate in the upper Gulf, they move to the central region to feed on large concentrations of sardines and anchovies (Dominguez-López et al. 2015). Predators presumably include larger fishes but also birds like the Eastern Pacific Brown Booby (Mellink et al. 2001).

Maximum size is 77 cm FL (Collette and Graves 2019). This species has a sex ratio of 1:1. Based on otolith ageing, the maximum age is eight years (Valdovino Jacobo et al. 2006). Based on the length-weight curve published by Valdovino Jacobo et al. (2006), the length at 50% maturity is 36.5 cm fork length (FL) at three years. The generation length is therefore estimated to be 3.8 years. In a study in the Gulf of California (Quiñónez-Velazquez and Montemayor-Lopez 2002), 442 specimens represented seven age groups, 0–5 males, 0–6 females. Maturity for males averaged 36.6 cm FL and 1.8 years, and females 38.3 cm FL and 2 years.

Because catches are reported as a combined group of both species of Spanish mackerels ("sierras"), it is difficult to determine a population trend for the Monterey Spanish Mackerel (Mexico National Fisheries Chart 2004). The fishery is apparently having severe effects on the remnant of the S. concolor population. Intense fishing pressure on spawning aggregations that are predictable in time and space appear to have led to rapid declines and the species is at risk of collapse (Quiñónez-Velazquez and Montemayor-Lopez 2002). Two other endangered species occur in the area, the Totoaba (Totoaba macdonaldi, family Sciaenidae) and the Vaquita (Phocoena sinus), a porpoise (Jefferson 2010, Sanjurjo-Rivera et al. 2021). It is important to note that the northern Gulf of Mexico has been heavily altered by the reduction of flow of the Colorado River (Brusca et al. 2017).

In the Upper Gulf of California, it is caught with another species of Spanish Mackerel, Scomberomorus sierra, mainly using gillnets close to the coast. The nets most used are 400 m long, 2 m wide, and set at an average of about 15 m deep (D' Agrosa et al. 1994). The commercial fishery operates from November to April in shallow coastal waters, bays, and estuaries and the combined catch of both species is 4,500 tons per year. Sport fishers catch both species of Spanish Mackerels (Collette and Graves 2019).

The Monterey Spanish Mackerel was last assessed as Vulnerable on the IUCN Red List (Collette et al. 2011). Survival of this species from overfishing by the gill-net fishery in the northern Gulf of California is linked to the survival of two more charismatic and more endangered species: the Vaquita (Phocoena sinus), a small endemic cetacean (Jaramillo-Jefferson 2010), and the Totoaba (Totoaba macdonaldi), a large sciaenid with a swimbladder worth more than its weight in gold. While there are no specific conservation measures for the Monterey Spanish Mackerel, restrictions on the gill net fishery for Totoaba in 1975 (Jaramillo-Legorreta and Taylor 2010) may have helped all three species survive. Establishment in 1993 of the Gulf of California Biosphere Reserve as a Marine Protected Area (Espinoza-Tenoria 2010) to protect the Totoaba and the Vaquita may also help protect the Monterey Spanish Mackerel, but the gillnet fishery is continuing for both species of co-occurring Spanish mackerels. To specify reference points for sustainable exploitation, population parameters for both Spanish mackerels are needed (Ramírez-Pérez et al. 2015).