Alosa chrysochloris (Rafinesque, 1820)
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Basis for Listing
The historical distribution of the Skipjack Herring (Alosa chrysochloris) in Minnesota was restricted to the Mississippi River downstream of St. Anthony Falls, Lake St. Croix and the St. Croix River downstream of Taylors Falls, and Big Stone Lake and the Minnesota River. The Skipjack Herring was last reported from Big Stone Lake (Big Stone County) in 1920 and persisted in Lake St. Croix (Washington County) until 1928. The loss of this species was attributed to the completion, in 1913, of U.S. Lock and Dam 19 at Keokuk, Iowa. This is the highest dam on the Mississippi River and became a barrier to the species' annual spawning migrations (Eddy and Underhill 1974). Consequently, populations declined dramatically, and this species was not reported in Minnesota for decades and was considered extirpated. Then, in the high-water year of 1986, the Skipjack Herring returned to Lake Pepin (Goodhue County), where several anglers caught adults and Minnesota Department of Natural Resources (MDNR) fisheries survey crews found young of the year (Hatch et al. 2003). Because of its rediscovery in the state and the documented evidence of successful spawning, the Skipjack Herring was listed as a special concern species in 1996.
The species continues to make rare appearances, though never in the numbers seen in 1986. In 2013, following the completion and analyses of targeted surveys (Schmidt and Proulx 2009), the status of the Skipjack Herring was elevated to endangered.
The Skipjack Herring is in the herring family (Clupeidae), which possesses a belly keel with raised scales producing a saw-tooth texture extending from the vent to the isthmus. The mouth is superior with teeth present on the jaws and tongue. The origin of the dorsal fin is forward of the origin of the pelvic fins. There are 17 rays in the dorsal fin, 18 in the anal fin, 20-30 gill rakers on the first gill arch, and 53-60 scales in the lateral series. Adults range in size from 25-45 cm (10-17 in.) total length and a maximum of about 55 cm (22 in.). Species similar in appearance and potential associates include: Gizzard Shad (Dorosoma cepedianum), Goldeye (Hiodon alosoides), and Mooneye (H. tergisus) (Lyons et al. 2012), all of which have hard to see teeth; Skipjack is the only one of these with a lower jaw that extends beyond the upper jaw.
The species prefers large deep and clear rivers with substrates of sand and gravel (Phillips, in preparation). In 1993 and 2011, five small specimens (2-15 cm [0.8-5.9 in.]) were sampled in Mississippi River Pools 4 and 8 from dam tailwaters, backwaters, and side channels. Habitats varied in depth 0.7-2.0 m (2.3-6.6 ft.), current 0-0.06 m/s (0-0.2 ft./s), and transparency 19-94 cm (8-37 in.) (LTRMP 2016).
Biology / Life History
Little is known of the spawning habits of the Skipjack Herring (Becker 1983). One early study near Keokuk, Iowa, found the spawning period to extend from early May to the first of July, but the species does not appear to congregate in large numbers, and spawning habitats were not observed. Skipjack Herring live for at least five summers (age 4), possibly longer. Young Skipjacks eat copepods and small larval aquatic insects, transitioning to larger larval and adult insects, minnows, and other small fishes as they grow, until small fishes become the predominant food (Robison and Buchanan 1988; Phillips, in preparation).
Conservation / Management
The U.S. Lock and Dam system on the Upper Mississippi River blocks the species annual spawning migrations, which now only occur at a fraction of historical levels, during prolonged periods of unusually high flows. Fish passage strategies have been discussed and proposed (e.g., an artificial channel bypassing U.S. Lock and Dam 3); however, these efforts have been abandoned with the arrival of invasive Silver Carp (Hypophthalmichthys molitrix) and Bighead Carp (H. nobilis).
Conservation Efforts in Minnesota
The Upper Mississippi River will not return, in the foreseeable future, to the free flowing system which this species requires to reproduce in Minnesota waters. Specimens, when encountered, should be examined for age and life history data, have tissue collected for genetic analysis, and have habitat parameters of collection sites recorded.