Identification of Ruffe larvae (Gymnocephalus cernua) in the St. Louis River, Lake Superior: Clarification and guidance regarding morphological descriptions.

Non-native ruffe (Gymnocephalus cernua; family Percidae) were first detected in the Laurentian Great Lakes in 1986, and are not included in regional larval fish keys which were published several years prior to their discovery. In addition, subsequent scientific literature has inconsistently described ruffe larvae. As a result, identification of larval ruffe remains challenging. We used traditional morphology paired with DNA technology to develop diagnostics for ruffe larvae collected in the lower St. Louis River, and compared them to similar species. We found that ruffe < 6 mm total length phenotypically resemble centrarchids, like black crappie, bluegill, and pumpkinseed, but have myomere counts that are intermediate between values for both common percid and centrarchid species. We suggest that developmental and pigment patterns as well as morphometrics can be used to distinguish ruffe from similar species at this size. At larger sizes, ruffe increasingly resemble other percids such as yellow perch, but can be distinguished using myomere counts and morphological features. The findings presented here clarify conflicting descriptions in the scientific literature, and provide additional data to support more confident morphological identification of larval ruffe.

Can a rapid underwater video approach enhance the benthic assessment capability of the national coastal condition assessment in the great lakes?

Over 400 sites were sampled in the nearshore of the U.S. Great Lakes during the U.S. National Coastal Condition Assessment (NCCA) field survey in summer 2010. Underwater video images were recorded in addition to routine NCCA benthic assessment measures. This paper has two objectives: (1) to develop a process to evaluate video performance with acceptance criteria, exploring reasons for poor images, and (2) to use acceptable videos in an example application with invasive mussels, evaluating the enhancement potential of video to supplement traditional grab sampling. A standard hierarchical protocol was developed to rank video performance based on quality and clarity. We determined controllable and uncontrollable factors affecting video performance. Moreover, specific thresholds limiting video were identified: >0.5/m for light extinction and >3.5 µg/L for chlorophyll a concentration. To demonstrate the utility and enhancement potential of video sampling, observed dreissenid presence from excellent (221 of 362 videos) videos was compared with NCCA benthic taxonomy, in the context of the statistically based NCCA survey. Including video increased the overall area estimate of the U.S. Great Lakes nearshore with invasive mussels by about 15% compared to PONAR alone; 44% (7570 km(2)) of the surveyed region had mussels. The proportion of the nearshore area having mussels varied from low (3.5%) in Lake Superior to >50% in the lower lakes. PONAR and video have unique strengths and weaknesses as sampling tools in the Great Lakes nearshore environment, but when paired were complimentary and thus provided a more thorough benthic condition assessment at lake and regional scales.