During translational surveillance, ribosomes play a critical role in detecting problematic mRNAs and signaling cellular machinery to repress the offending messages. Prior work has shown that problematic mRNAs identified by two surveillance pathways (Nonstop and No-Go mRNA Decay) are detected by ribosome collisions and subsequent ribosomal ubiquitination, yet how ribosomal ubiquitination leads to repression has remained unclear. Here, we deploy C. elegans to unravel the series of coordinated events during Nonstop and No-Go mRNA Decay. We probe the metazoan SKI RNA helicase complex to uncover functionally significant residues and reveal divergence of the SKI-exosome interface. We define a functional requirement for ubiquitination on at least two ribosomal proteins during No-Go mRNA Decay, and illustrate how ubiquitination recruits the endonuclease NONU-1 via CUE domains and the ribosome rescue factor HBS-1 via its poorly characterized N-terminus. Our molecular characterization (1) underscores the importance of ribosomal ubiquitination in mRNA degradation, (2) shows similar and distinct genetic dependencies of factors in Nonstop and No-Go mRNA Decay, and (3) uncovers a conspicuous absence of distinct ribosomal stalls at No-Go mRNA Decay substrates. Our work demonstrates mechanisms by which translation signals to effectors of co-translational mRNA repression and has implications for the study of translation and ribosomal species in vivo.